Quick fire making using sunlight.

Quick fire making using sunlight.

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

(Blog No.44).
#make fire, #making fire, #fire, #Sun, #sunlight, #crystal, #glass #ball, #sphere, #lens, #ocular, #monocular #sun-rays, #survival.

You may already have in your possession some excellent lenses for making fires. Knowing about them will help you make fire quickly from sunlight when facing an emergency. All lenses described in this blog can make a cigarette smoulder in less than 30 seconds and can light up that cigarette afterwards.

1. Concentration of radiating heat flux by a lens.

The radiating heat flux from the Sun is concentrated by a factor C given by

C = Pi*d*d/(Pi*f*a*f*a) =

C = (d/f)*(d/f)*(1/a)*(1/a).

where d and f are respectively the diameter and focal length of the lenses and a is the angular diameter of the Sun (a = 0.5*3.14/180radian = 0.0087 radian).

The angular diameter of the Sun cannot be changed. It is obvious that we have to increase the ratio (d/f), which is called the aperture number of the lenses, to increase the heat flux concentration. The deciding factor for success is the aperture ratio of the mirror or lens system.

C = 13200*(d/f)*(d/f).

This concentration of heat flux is remarkably high for any lens system with D/f of more than 1/3 and can be used to ignite properly prepared tinder to make fire in survival situations.

The calculated concentration of radiating heat flux can only be achieved using precision optics. Any imperfection on the surface of the lens disperses the image of the Sun and reduces the concentration drastically.

2. A transparent perfect sphere.

crystalballc70.jpg

Figure 1 : A small clear sphere (25mm diameter).

crystalball2c70.jpg

Figure 2 : Small clear sphere (close up view).

You may have a small clear glass sphere somewhere in your household either as a decorative item, or as a bottle stopper, etc…

The small transparent sphere I use here is a small (25.4 mm diameter) clear quartz sphere often used as an item of curiosity and often called a “crystal sphere” by fortune tellers.

Calculations using geometrical optics show that (for n=1.5) the focal point is about 0.5 radius outside the surface of the ball and the equivalent focal length of the sphere is about 2r×(3/4)= 1.5r

Even if only rays of distance less than 0.5 radius (from the central ray) converge on the spot, the aperture of the sphere is still
D/f = (2*0.5r)/(1.5r) = 1/(1.5),

a high value for aperture.

At an aperture value of 2/3, the concentration of radiating heat by sunlight is

C = 13200*(D/f)*(D/f) = 6000.

The actual aperture number of this clear sphere is higher than 1/1.5 and the sphere can be used as a lens to light up cigarettes using sunlight.

Figures 3 : Lighting a cigarette by a small 25mm clear quartz sphere.

The above photo also demonstrates the danger of leaving clear glass balls on any combustible surface. When the afternoon Sun comes down to an elevation of 41degree (= arcsin 0.6666), the image of the Sun is exactly on the combustible material and combustion becomes a real possibility !

The concentration factor of C = 6000 is only realized with a perfect sphere. For any body of revolution of nearly spherical shape, the concentration of radiating heat flux is much lower, and may come down to C = 100 when there is some appreciable astigmatism. For this reason, PRECISION IS MORE IMPORTANT THAN SIZE for transparent spheres.

I prefer having a small perfect sphere to a large approximate sphere.

3. A watchmaker double staged ocular.

Figure 1: A watch maker monocular.

Figure 2 : A watch maker monocular (rear view).

Figures 3 : Lighting a cigarette by a watch maker monocular.

A monocular is a compound magnifying lens used by watchmakers to see small details of watch movements. It is a simple version of the oculars used for each eye in common sport binoculars.

Every first aid kit for hikers should have this light weight and useful device and a pair of sharp tweezers for detecting and removal of hurting spikes or splinters sticking in the skins.

The lens nearer to the eye of a proper ocular has a large diameter to give the eye a wide field of view. The double stage makes tiny object has a large image at infinity.

When sunlight travels in the reverse direction from the back (big) end to the front (small) end it will focus at a tiny spot outside the ocular and about 20mm from the front lens.

The aperture ratio D/f of this compound lens is about 1/2.

If the dark end of a cigarette is placed at that bright tiny spot smouldering will begin in less than 1 second on a sunny day.

If the oculars of your binoculars are thread removable then you can also use them in emergency but keeping in mind that taking apart a pair of binoculars will allow dirt to contaminate it.

The concentration factor of C = 13200*(d/f)*(d/f) is only realized with a lens having perfect spherical surfaces. For any lens with only approximate shape, the concentration of radiating heat flux is much lower, and may come down to C = 100 when there is some appreciable astigmatism. For this reason, PRECISION IS MORE IMPORTANT THAN SIZE for any monocular.

I prefer to have a small quality monocular than a large one with low quality.

4. Aspherical condenser lenses.

Figure 1: A fused quartz aspherical lens.

Figure 2: Fused quartz aspherical lens viewed from another direction.

I was lucky to be given a fused quartz, thick aspheric lens. Its aperture ratio is about D/f=1/1.5 while other thin spherical, glass lenses have a ratio of less than 1/2.5.
The concentration of solar heat flux is much higher when using it than when using an ordinary magnifying glass.

Figure 3: A one battery LED torch with a thick aspherical lens at the front.

The front lenses of zoom focus LED torches are low cost substitutes for such aspherical lens. They do work exceptionally well and are even unbreakable since they are made from (acrylic ?) plastic.

Disadvantage.

The disadvantage of using any such aspherical lens for making fire is that it is heavy and it has very short distance from its flat side to the bright focal point. Sunlight coming to this bright focal point from many widely separated directions and it is difficult to direct them all to the trough of the dimple at the center of the end of a cigarette. I found that it is less easy to light up a cigarette using an aspherical lens than using a good monocular of the same diameter.

Again, it is important to also note that PRECISION IS MORE IMPORTANT THAN SIZE for any aspherical lens.

I prefer to have a small quality aspherical lens than a large one with low quality.

5. A flexible Fresnel lens for wallet.

Figure 1: A thin flexible Fresnel lens for wallet. Concentric grooves can be noticed at the right hand corners of this picture.

The lens is usually made of thin, flexible, soft clear plastic of the size of credit cards. This type of lenses is sold as wallet sized magnifying glasses for map reading.

A Fresnel lens has high aperture ratio and can be used to light up cigarettes with ease. However it needs to be properly cleaned after each use as it is easily scratched.

6. Method of lighting up a cigarette using a small lens.

1. A cigarette or its imitation made up from rolled up toilette tissue sheets with darkened ends seems to be the readily available suitable tinder sticks for making fire using sunlight.

2. A conical dimple should be made at the dark end of a cigarette. The depth of the dimple should be about the size of its radius. That is a conical concave surface should be made out of the dark flat tip of the cigarette. This tiny concave surface reduces radiating heat loss from the fire to be started at its trough.

3. A precision lens is used to focus sunlight onto the dark end of a cigarette. PRECISION IS MORE IMPORTANT THAN SIZE as the high concentration of sunlight depends on precision of the lens surface.

4. The axis of the lens system should point exactly at the Sun to have maximum amount of sunlight converging on the focal point.

5. Sunlight should be focused on one point on the surface of the dimpled end of the cigarette to blacken it. Smoke should be seen arising from the spot within 10 seconds after focusing. Other points of the surface should then be smothered to have all the surface gradually blackened.

6. Sunlight is now focused on the trough point of the dimpled surface. Smoke will be seen and the trough will glow red when assisted by gentle wind blowing toward the other end of the cigarette.

7. The cigarette should now be smoked or blown externally so that hot fume from the flame end travels toward its other end to heat up the adjacent zone to ready it for combustion.

8. A strong red glow indicates that the cigarette has been burning. It can now be used to start up a fire.

References

[1]. tonytran2015, Making fire and lighting cigarettes with sunlight, survivaltricks.wordpress.com, Making fire and lighting cigarettes with sunlight, posted on February 27, 2016

[2]. tonytran2015, Mirror for making fire using sunlight, survivaltricks.wordpress.com, Mirror for making fire using sunlight, posted on April 13, 2016

Appendix: Calculations for the spherical lens.

The focus point is about 0.5 radius outside the surface of the ball. D/f is about 0.7.
Front face

1/f = (n-1)(1/r1 + 1/r2)
f = r/(n-1)

f = 2r front

Let d be the distance from the front surface to the focal point.

d = r/(n-1) in air, rn/(n-1) in glass

d=2r in air, 3r in glass
Let d1 be the distance from the Rear surface to the focal point to.
d1 = rn/(n-1)-2r = r(-n+2)/(n-1) in glass,

r(-n+2)/(n×(n-1)) in air

d1 = r in glass, 2r/3 in air

1/d2 = 1/(2r) + (n×(n-1))/( r(-n+2) )

=(1/((2r)× (2-n)))×(2-n+2n×(n-1))

1/d2= (1/((2r)× (2-n)))× (2n*n-3n+2) for n=1.5,

1/d2 = 1/(2r) + 3/(2r)
d2 = 0.5r

Rear magnification:

0.5/(2/3) = 3/4

Equivalent focal length of the sphere is

2r×(3/4)= 1.5r
Calculations using geometrical optics show that for n=1.5 the focal point is about 0.5 radius outside the surface of the ball and the equivalent focal length of the sphere is about

2r×(3/4)= 1.5r

Aperture is

D/f=4/3.

Obviously actual parallel rays at one radius distance from the axis of the ball cannot converge on the bright spot.
Note that the radiative heat flux from the Sun is concentrated by a factor C given by
C = Pi*d*d/(Pi*f*a*f*a) =
C = (d/f)*(d/f)*(1/a)*(1/a).
where d and f are respectively the diameter and focal length of the lenses and a is the angular diameter of the Sun (a = 0.5*3.14/180radian = 0.0087 radian).
The angular diameter of the Sun cannot be changed. It is obvious that we have to increase the ratio (d/f), which is called the aperture number of the lenses, to increase the heat flux concentration. The deciding factor for sucess is the aperture ratio of the mirror or lens system.
Even if only rays of distance less than 0.5 radius converge on the spot, the aperture of the sphere is still

D/f = (2*0.5r)/(1.5r)

= 2/3 = 1/(1.5),

a high value for aperture.

At D/f of 2/3, the concentration of solar heat is

C = 13200*(D/f)*(D/f) = 6000.

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Making fire and lighting cigarettes with sunlight. Posted on February 27, 2016

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Making fire and lighting cigarettes with sunlight

Making fire and lighting cigarettes with sunlight

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

#make fire, #making fire, #fire, #Sun, #sunlight, #sunray, #lens, #magnifying glass, #mirror, #survival.

StormWatchDiagram

Figure 1: Diagram of making fire by a mirror.

StormWatchBurnsCig

Figure 2: Lighting a cigarette by sunlight. Smouldering is visible after 27seconds.

I used here

1. a device consisting of a lens and a mirror right behind it (see following pictures),

2. then another alternative device being the dial face of an unusual Storm brand Remi watch (in the above pictures).

The combination of a lens and a mirror right behind it produces a large aperture system giving high power concentration and it also has light weight and convenience for cigarette lighting. My 60mm lens and mirror system with aperture ratio of d/f =60/65 = 1/1.1 regularly makes cigarette fire in 15seconds.

The Storm brand watches has an interesting unusual Remi model that has a mirror face with 2 small and 6 tiny windows for displaying painted numerical hours, minutes and fraction of a minute. The rest of the face acts like a concave mirror of 38mm diameter. The pictures show one such watch I could get hold of. The equivalent mirror has a focal length of 75mm (aperture ratio of d/f = 1/2.5) and I had been able to use it to light up a normal (dry, not wet) cigarette in less than 60seconds!

Having a lit cigarette is having a fire on hand.

The advantage is that a normal cigarette can be lighted on any sunny day in 5 minutes with minimal set up.

The disadvantage is that smoking is harmful to your health. You have to light up a cigarette but smoking it is not encouraged !

The steps are described in details as in the following.

1. Selecting a magnifier with large aperture.

MagnifierMirror

Figure 1: A mirror attached to a 60mm clear, colourless glass lens. This system with aperture ratio of d/f=1/1.1 can light up a cigarette in only 15 seconds. This is my favourite set up.

SphericalSpoonForBurning

Figure 2: Even a polished spherical soup spoon with high aperture ratio can also light a cigarette.

It is shown here the success of this method depends on having a high aperture ratio.

The concentration of sun-ray heat is proportional to the square of the aperture of the lens and mirror system. Concentrated heat burns fuel easily. Select a lens and mirror system with a large aperture (high ratio of diameter to focal length) for fire making by sunlight.

A reflective mirror right behind a convex lens nearly doubles the aperture ratio of that single lens and increases concentration of power by nearly four times around the new focal point (on the Sun’s side).

Transmission media absorb energy. Select magnifying glass made from clear, colourless material. I found that clear, colourless glass is best for this purpose.

Only 40% solar radiation energy is in visible sunlight, the other 10% and 50% are in Ultra Violet and Infrared respectively. Some materials may not allow these part to pass through in the same way as visible light. The choice of materials is thus important in making collimated solar power.

Aperture ranking of various systems:

The aperture ratios of familiar systems are

d/f = 1/1.1 for the system in the pictures (lens plus mirror),

d/f = 1/1.5 for the aspherical, plastic front lenses of most focusing LED torches,

d/f = 1/2.5 for the Storm watch,

d/f = 1/2.5 for common magnifying glasses with medium thickness,

d/f = 1/4 for common magnifying glasses with thin thickness.

The spoon head in use here is almost a concave spherical mirror with quite high ratio of d/f=1/0.4 . However it does not light up the cigarettes very quickly as expected because it is not an ACCURATE mirror and the picture of the Sun at its focal surface is not clearly defined and too spread out.

It takes 12sec, 15sec and 40seconds to light up a cigarette using that spherical spoon (when WELL POLISHED), the lens with attached mirror (in the picture) and the Storm watch respectively. When the spoon was dull and unpolished, it took up to 120 seconds to light the cigarette.

A common, colourless, thin magnifying glass with d/f = 1/4 can still make a well prepared cigarette/tinder stick smoulder (in less than 5 seconds) using sunlight from even a late afternoon Sun at low (20 degrees) elevation.

Even a small, 16mm diameter, plastic front lens with d/f=1/1.5 of a focusing LED torch (powered by a single AA-battery, pictured at the end of the article) has been successfully used to consistently ignite (in less than 5 seconds) my well prepared charred stick of rolled up (10cmX10cm) sheet of toilette tissue by focusing afternoon sunlight (from the Sun at 30 degrees elevation, in a clear sky) onto it.

2. Alignment

StormWatchDiagram

Figure 1: Aligning the Storm watch and the cigarette for making fire.

StormWatchFront

Figure 2: Front view of the unusual Remi model of watches by Storm.

Align the axis of the watch toward the Sun.

From the 3 o’clock direction of the watch (in front of the dial windows which do not reflect much sunlight), hold a normal (dry, not wet) cigarette to have its tip reaching the focal point.

It may help to have the mirror axis pointing slightly from the Sun so that the cigarette and the hand holding it cast no shadow on the mirror.

The cigarette should be nearly parallel to the watch dial. The butt of the cigarette should be slightly away from the dial and the tip should be near the focal point and be brightly shone by collimated sunlight reflected by the mirror dial.

If a concave mirror or a lens is used instead of the above watch, align its axis towards the Sun to minimize the picture at its focal plane.

3. Focussing

The distance from the tip of the cigarette to the center of the dial should be varied until the reflected sun-rays is collimated into the smallest spot on the dark tobacco cuttings (fibers) at the central axis of the cigarette. Do not focus sun-rays on the enveloping white paper as white objects bounce back more radiative heat than dark objects.

WARNING: Prolonged looking at the concentrated (focused) sun light reflected off white enveloping paper of the cigarette may injure your eyes.

4. Smouldering needs time.

StormWatchFocussng

Figure 1 : Lighting a cigarette by the Storm Watch at 27sec.

SphericalSpoon

Figure 2 : Lighting a cigarette by a spoon 12seconds.

Figure 2 shows smouldering using the polished, spherical head of a stainless steel soup spoon.

Keep the center of the cigarette tip so heated (by collimated, reflected sun rays) for about 3 minutes until there is sign of smouldering with steady smoke rising from it.

Smouldering takes 5sec and 12sec respectively for system of the lens plus mirror and for the WELL POLISHED spherical spoon. The spoon does not have an accurate spherical shape and its reflected sunlight is not well focussed.

5. Turning smouldering into fire by gentle wind

For smokers: Suck air in through the butt of the cigarette to intensify the smouldering into a red glow of cigarette fire.

For non-smokers: Directing your gentle air blow from the tip to the butt of the cigarette may also have the same effect.

Due to the required flow of hot fume through the inside of the cigarette, it is best to start the smouldering with sun rays on the dark material at the tip of the cigarette to start smouldering then slowly tilt the cigarette at angle, keeping the smouldering, to have sun rays heating the hot spot through the side while hot fume can go up inside the cigarette and exit at the other end.

This method of lighting a normal cigarette by sun rays using the watch face has been actually tested successfully on a dry (Summer) day at 15hr, on November 11th, 2015 in Melbourne (39 degree South in latitude), Australia. It has been successfully repeated on many subsequent sunny, dry days.

A roll of tinder made of dried fibers or charred cotton may be used instead of a cigarette. However cigarettes seem to be the best rolls of tinder readily available for this method of making fire.

A rolled up sheet of well crumbled newspaper material (non-gloss material with loosely adhering fibers) in the shape of a long cigarette may partially provide the flammability of a cigarette and may also be used here instead of the cigarette. You may expect longer time to smouldering in this case.

Note:

A smouldering rarely turns into a cigarette fire without AIR FLOWING FROM THE TIP TO THE BUTT INSIDE the cigarette.

6. Making a stick of tinder for making fire by sunlight.

TinderToiletTissue.jpg

Figure 1: A rolled up sheet of toilette tissue to be made into a tinder stick. Inset: The remaining last third of such a stick after ignition started by concentrated sunlight from a magnifying glass.

TinderCharredTissue.jpg

Figure 2: A stick of rolled up toilette tissue with charred end.

A stick of tinder can be made by rolling up moderately tightly a 20cm long sheet of toilette tissue into the shape of a long cigarette. A DARK MARKING of more than 2mm diameter should be made with a pen or a ball pen on the outside surface of such a stick to let it absorb sunlight heat to start the smouldering. Such a stick burns almost like a cigarette when externally blown with steady, gentle, fresh wind.

Loose rolling allows the fume to flow inside the stick from the fire end to the other end to heat up and deposit flammables on the next section of tinder, readying it for the fire but may make the fire propagate unevenly across the cross section of the stick. Tight rolling gives the fire time to spread evenly across the cross section but may restrict the flow of the fume to heat up and deposit flammables on the next section of tinder. An optimal balance can be found between the two extremes by fine tuning the tightness in rolling.

A tightly rolled up sheet of crumbled newspaper material (non-gloss material with loosely woven fibers) in the shape of a long cigarette may also make an alternative (but admittedly poorer) substitute for a cigarette. A DARK MARKING of more than 2mm diameter should be made with a pen or a ball pen on the outside surface of such a stick to let it absorb sunlight heat to start the smouldering. You may expect longer time to smouldering with this roll.

A roll of broken dried leaves inside a rolled up dried leaf can also be used as a (poorer) substitute for a cigarette. The enveloping leaf may get slightly broken when rolled up. The broken dried leaves inside the roll should be tightly packed (and even refilled and compacted again and again after rolling the enveloping leaf) to be able to maintain the smouldering. A DARK SPOT of more than 2mm diameter should be created on the side surface of the roll to let it absorb sunlight heat from the side for smouldering so that fume can flow upwards inside the roll. You may expect longer time to smouldering with this roll and you may have to exert a lot of wind blowing onto the tip of the roll to intensify the smouldering into a red glow.

Commercial cigarettes seem to have been optimized for such burning and appear to be best (although costly) for use as tinder sticks. A stick of rolled up toilette tissue ignites and burns as well as a fresh cigarette. A stick of rolled up crumbled newspaper is a close replacement. However, a stick of fake cigarette or fake cigar made from broken dried leaves inside a paper roll ignites very poorly due to loose packing.

Without the dark spot, the time to smouldering for a rolled up sheet of toilette tissue is more than 20 times the corresponding time with the dark spot. I suppose that the white tissue reflect more than 97% of sunlight heat while the dark spot allows it to absorb about 50% of sunlight heat.

Making a charred stick of tinder out of a rolled up sheet of toilette tissue.

A charred tinder is made up of almost pure carbon. It has higher ignition temperature, but it does not conduct heat and it is black, absorbing sun ray heat most efficiently. Since it absorbs sunlight heat and has poor heat conduction, its temperature can rise quickly past its spontaneous combustion temperature when shone by concentrated sunlight. It is thus most suitable material for starting fire with sunlight, burning even with a moderately concentrated beam.

A well prepared charred stick of rolled up sheet of toilette tissue can even be ignited by using only a small, plastic, 16mm diameter front lens of a LED torch to focus afternoon sunlight (from the Sun at 30 degrees elevation, in a clear sky) onto it.

Any combustion of organic materials is a combination of many competing chemical reactions. By reducing the concentration of oxygen in the surrounding gas, the burning of carbon can be drastically reduced while the decomposition of organic compounds into carbon, hydrogen, oxygen and nitrogen can still proceed, producing a skeletal frame, made entirely from carbon, of the material. This gives a charred object in the shape of the original object.

A charred stick of tinder can be made as in the following:

Make a red glow at one end of the stick (with a magnifying glass or with another source of fire). Hold the glowing end of the stick downward, stick it into the center of a fully blown up, clear bag of poly-ethylene (of 500mL of 1000mL capacity), away from the wall of the bag, and twist the open end of the bag around the stick to keep the bag pressurized and the red glow away from its wall, then keep twisting past the stick. The result is a closed blown up bag with a tinder stick burning inside it, away from the wall. After about 1 minute, the inside of the bag is starved of oxygen and the red glow reduces to a low temperature fire charring it adjacent material. Wait for 10 minutes for any fire to extinguish then take the stick out of the bag. One such stick with a charred end is illustrated in the figure.

7. Some unusual but fast ways to light up a cigarette for making fire.

FireFromSpoon

Figure 1: Lighting a cigarette by a WELL POLISHED spherical spoon head with d=50mm, f/d=1/0.4 at 12s, 9s, 7s, 4s, 0s.

FireFrKeyRingMagnifier

Figure 2: Lighting by a small glass lens with d=21mm, f/d=1/2.5 at 16s.

8. Making fire with a serving spoon and a cigarette.

FireFrNewSoupSpoon

Figure: Reverse sequence of burning a cigarette by a 60mm, POLISHED, SPHERICAL serving spoon at 37s second. This spoon has a very high aperture ratio, D/f = 3.5.

An insulated copper wire has been wound on the handle of the 60mm, POLISHED, SPHERICAL serving spoon to hold the cigarette. The focal point is on the plane defined by the rim. No blowing is necessary with this large system. The smouldering turns into a cigarette fire by itself.

This was carried out in Vietnam (Saigon) on December 14 (mid-winter) under a clear sky; air temperature was 30degree C, the air was dry and the elevation of the Sun was 55degrees. The cigarette brand was Craven, readily available locally, with light brown leaves.

The cigarette can also be replaced by a stick of rolled up 20cm sheet of toilette tissue (with a DARK MARK made on the end or the edge of the end to absorb heat of collimated sunlight).

Selecting a spoon for collimating sunlight.

The easiest choice is with spoons having spherical spoon heads. The chosen spoon head should be well polished and should have shiny reflections. The focal point of any spherical surface is one half (1/2) of the curvature radius from the surface.

From a distant point on the spoon head’s axis, a very small spot on the cigarette tip placed at the focal point should be seen magnified to be bigger than the whole spoon head. All sunlight reaching the spoon head will travel backwards along those paths into that small point at the tip of the cigarette to heat it to high temperature.

For any common elongated spoon head, put the tip of a pencil at the estimated focal point and look at the spoon head from various directions. If any small part of the of the tip can be seen to be magnified to occupy more than 40% of the surface of the spoon head from some direction, it is possible to use such spoon head to heat up a small part of the tip using the sunlight coming from the viewing direction. The spoon must pass this test before you can try to ignite anything using its collimated sunlight. (Most common elongated spoon heads do NOT pass this test.) For common elongated spoon heads which have passed the test, the Sun usually has to be offset 60 degrees from the normal axes of the spoon heads for making fire. Only elongate spoon heads which can easily light up traditional match heads using sunlight should be experimented in lighting cigarettes/tinder sticks.

9. Notes on making fire by a magnifying glass.

MagnifierLEDTorch

Figure: Making fire, even with a small, 16mm in diameter, plastic front lens of the focusing LED torch (powered by one single AA battery) in this picture can be consistently carried out by igniting (to make fire) in less than five seconds a well prepared charred stick of a rolled up (10cmX10cm) sheet of toilet tissue (ambient temperature was 34 degrees C, humidity 30%, elevation of the Sun was 30 degrees in the tests).

Users of this method should remember that:

1. The radiative heat flux from the Sun is concentrated by a factor C given by

C = Pi*d*d/(Pi*f*a*f*a) =

C = (d/f)*(d/f)*(1/a)*(1/a).

where d and f are respectively the diameter and focal length of the lenses and a is the angular diameter of the Sun (a = 0.5*3.14/180radian = 0.0087 radian).

The angular diameter of the Sun cannot be changed. It is obvious that we have to increase the ratio (d/f), which is called the aperture number of the lenses, to increase the heat flux concentration. The deciding factor for sucess is the aperture ratio of the mirror or lens system.

2. As a concave mirror is expensive, a cheaper equivalent made of a lens plus a mirror right behind it is often in use. This alternative is also lighter and more convenient to use than a thick lens in lighting cigarettes.

3. It has been carried out on a summer day with a lot of sunray heat per square meter area. The steady focussing is essential and the method may not be suitable on a unsteady platforms such as boats, ships, trains …

4. It has been carried out in a dry day.

5. The cuttings of leaves inside the cigarette (acting as fuel, tinder) should have dark colour to absorb sun ray heat

6. Gentle sucking is required to intensify a smouldering into a fire. Blowing air out from the butt of the cigarette may not intensify the fire.

7. To check the sphericity of the head of the spoon, you have to look at your own upside down reflection inside the spoon head. Till the spoon in various direction to have your reflection moved from the center to various sides on the edge. The spoon head is spherical if your picture does not expand or shrink during the test.

Some unusual sources of fire and unintended fire can be found in the references.

References.

[1]. Anonymous Author, Brigade step up sunlight warning after another refraction blaze, London Fire Brigade, http://www.london-fire.gov.uk /news/LatestNewsReleases_warningassunstunscelebrity.asp#.VndyHOW4ZAg, 26 February 2015.

[2]. PF Louis, Metal dog bowls can start house fires from focused sunlight reflections, Natural news , http://www.naturalnews.com/040979_dog_bowls_house_fires_… href=”http://www.naturalnews.com/040979_dog_bowls_house_fires_fire_prevention.html”> http://www.naturalnews.com/040979_dog_bowls_house_fires_… ,June 28, 2013

[3]. Matt Payton, Jar of Nutella destroys family home and kills pet dogs, Metro.co.uk ,

http://metro.co.uk/2015/02/23/nutella-jar-helped-sun-rays-set-fire-to-family-house-and-kill-pet-dog-5076204/ ,23 Feb 2015.

[4]. Peter Lappin, Working on My Linen Shorts + How I Nearly Burned the House Down, Male pattern boldness, http://malepatternboldness.blogspot.com.au/2014/0… , Aug 18, 2014.

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Finding North and time by stars. Posted on August 28, 2015

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