Remembering that a lens would concentrate the sun's rays, he concluded that with his glass he might start a fire, and in this he succeeded.
Almost exhausted, he dragged himself back to his last camp, and there, fortunately, the lens was found.
The one that I select is at present one of the most enigmatical cases known, namely, the regeneration of the lens of the eye in the tadpoles of salamanders.
In the normal development of the tadpole from the egg, as in all other vertebrate animals, the lens is formed from the outer skin or ectoderm of the head.
What fills the embryologist with astonishment is the fact that the new lens is not formed in the same way or from the same material as the old one.
In the replacement of the lens after removal it arises from the cells of the iris, which form the edge of the optic cup, and this originates in the embryo not from the outer skin but as an outgrowth from the brain.
If the lens be removed from the eye of a young tadpole, the animal proceeds to manufacture a new one to take its place, and the eye becomes as perfect as before.
I place the glass lens in a microscope, and a hitherto unknown world is revealed to me.
But now another question: Do I see with the lens which is a part of my eye?
It is evident that the lens is merely an aid to vision, since the lensin my eye is also necessary to convey the picture to my mind.
The glass lensis merely a supplement to the lens of the eye.
It is one step further removed from the vision, but even the lens of the eye itself is not the seeing power.
This lens, in its shape, resembles a certain other lens through which I look in examining it.
He placed his magnifying lens between the electric flash and the paper, and now the uneven strokes dissolved into uncouth but fairly legible letters.
He took a magnifyinglens from his kit and carefully examined the surface.
We therefore erected a frame over the gun, and fitted the lens of a camera on an axle placed due east and west, so that it could turn in the plane of the meridian, and so be adapted to the sun's gradual change of declination.
We first place our sand on a sheet of white paper, and with our pocket lenshave a thorough examination of the various constituents.
In countries where the sun shines continuously, a burning glass, such as the lens of a telescope or a Stanhope microscope, will obtain fire at any time during the day.
The form and structure of the crystalline lens endow it with a remarkable degree of refractive power, and enable it to converge all the rays of light that enter it through the pupil, to a focus exactly at the surface of the retina.
From this we learn that one of the uses of the crystalline lens is to make the retinal image bright and sharply-defined, at the same time that it reduces its size.
The front face of the lens is flatter than the other, and is in contact with the iris near its pupillary margin, as is represented in the diagram on page 214.
In practice, however, it is found better to use several magnifying glasses of moderate power, than a simple lens alone of high power.
Between the crystalline lensand the cornea is a small space which contains the aqueous humor (see Fig.
When the eye is at rest, that is, when accommodated for a distant object, the lens is flatter and its curvature diminished (see Fig.
A convex lens has the property of converging the rays of light which pass through it; and the point at which it causes them to meet is termed its focus.
That part of the globe of the eye lying behind the lens is occupied by the vitreous humor, so called from its fancied resemblance to melted glass (Fig.
The left half shows the lens accommodated for near vision.
The horse, on the other hand, sees with all parts of the lens simultaneously, in so far as the lens is not covered by the iris.
On a spherical surface linear movements of a point of light are always imaged as curves, no matter what the shape of the lens forming the image may be.
This imperfection consists in an irregular formation of the sclerotic coat and of the lens of the eye.
The arcuate deflection, which is nothing but a registration of the difference in the indices of refraction of the different parts of the lens used consecutively, might thus be formed for the observer using the mirror, but never for the horse.
It was with great difficulty that a sufficient number of photographic lenses was obtained for the use of military cameras, since the large lens factories of America were tied up with other war orders.
To emphasize the contrast, the camera lens was covered with a reddish colored ray filter, and this brought out sharply the outline of the streak.
It was evident that we must provide eyepieces which would not break easily, since even so slight an accident as the breaking of a lens might cost a soldier his life by admitting concentrated gas to the mask.
Keuffel & Esser had made many prismatic compasses and a few range finders; the Spencer Lens Co.
In December, 1917, the work was extended, men from the Geophysical Laboratory taking practical charge of the plants of the Spencer Lens Co.
The capture of the entire city of Lens was then only a matter of time, as Hill 70 insured the holding of the ground won by the Canadians, German reinforcements being placed under the range of irresistible fire from that dominating height.
The British were continuing their pressure on both Lens and St. Quentin, but were temporarily held up by a great storm on the 16th.
It was on this hill that the British forces under Sir John French were badly broken in their efforts to reach Lens in the first battle of Loos, in September, 1915.
With the centre B (the compass leg being in all cases placed with absolute accuracy, using a lens if necessary to place it) describe the circle C D E.
These lose very much by reduction, and should be seen with a lens magnifying 2-1/2 diameters.
The center of the lenswas gone and only a little on each edge remained.
After examining my eye he said there was one-third of the lens of my eye entirely destroyed.
Fortunately it was not a Muzzle-loader, so they have been able to put a Lens at both Ends.
It may be seen very plainly by the naked eye, but under a good lens increases in interest.
After a few hours it will settle down, and a lens will assist in the detection of whatever curiosities may swarm out of the refuse weed.
Sometimes we take off the film of a cataract from the eye; sometimes even we can take out the crystalline lens and substitute a heavy lens in glasses to be worn by the patient.
Then there was spread across the aperture of your lens an opaque granulated curtain through which light could not pass.
The lens is mounted on a pivot and when the exposure is to be made, by pressing a lever the lens automatically swings on this pivot from one side of the camera to the other, embracing an angle of over 100 degrees.
Kodak and be sure to specify the shutter that the lens is to be used with.
Illustration] Both cameras offer the usual Kodak simplicity, and the exceptional lens and shutter equipment which assures the user the maximum of efficiency in all work where an anastigmat equipment is not necessary.
The lens is a Rapid Rectilinear of the same high quality as those supplied with the preceding Kodaks.
In both cases the lens is carefully tested and must conform to the high Kodak standard before it is allowed to go on the camera.
Each is fitted with the Zeiss Kodak Anastigmat lens working at a maximum opening of f.
Again, in making a landscape, the sweep of the Panoram lenswill take in the complete view, while the scope of the ordinary camera could only permit a portion of it to be taken at one exposure.
For average photography, the camera fitted with Kodak Ball Bearing shutter and tested meniscus achromatic lens is amply efficient, for it will make excellent pictures under ordinary conditions.
This lens is an anastigmat of first quality, fully corrected and working at a maximum speed of f.
The speed of a lens is determined by the relative size of the diaphragm opening.
The attachments are simply extra lenses, which slip on in front of the regular lens, and they in no way affect the operation of the instrument, excepting to make the lens cut sharp at short distances.
This shutter, which turns a reflectinglens on the harbor, can be turned in any direction.
Overhead is a revolving shutter, somewhat on the plan of a camera's lens shutter.
A pocket lens or a tripod lens is desirable, but not a necessity.
Observe the flowerets through a lens if you have one and note that the pollen sacs open a little at one side instead of at the tip so that the wind is needed in order to shake out the pollen.
Look at snow crystals through a tripod lens if you have one.
A good hand lens will show the embryo branch, if a section is made of the bud.
Even fine loamy and clay soils, when examined with a pocket lens or a microscope, will be found to be composed of tiny fragments of mineral.
The use of a simple lens often contributes much interest to the work of observation.
But good sharp eyes are sufficient if no lens is available.
If a pocket lens or a reading glass is to be had it will add to the interest, as more of the details can be observed.
A reading-glass or lens may be used to advantage in making these observations.
If the teacher has a lens the children should view the eggs through it.
The head to this drum is of parchment thrown into folds and may be seen with a lens if you lift his wings and look closely.
One eye showed fracture of lens, the other lens showed fine lines.
Careful examination, however, by a small lens if necessary, is sufficient to distinguish them if they are fresh.
In their general advance onLens the Canadians occupied the strongest outpost in the defense of that place, and pushing their troops on toward La Coulotte, entered that village.
Craters which had been made by mine explosions at the crossroads, seriously hindered them in bringing up troops from Lens for counter-attacks.
This was speedily followed by heavy artillery fire, which continued during the night in the vicinity of the Lens electric station.
Patrols which were sent out reached the summit of Reservoir Hill without opposition and pushed on down the eastern slope and the strong Lens outpost was effectively occupied.
But by providing the loop an elastic feed is secured, and the film is jerked into position before the lens with the minimum of vibration and without any risk of tearing or displacement.
With the 2-inch Zeiss-Tessar lens of the Williamson camera when the largest aperture is used, nothing important in the picture should be within a distance of 20 feet.
When very rapid movements are being investigated these losses become appreciable--in fact the most vital part of a motion may be missed during the 1/32 part of a second during which the lensis covered by the shutter.
His complete outlay upon the camera and the lens need not exceed L6 5s.
What occurred while the lens was shut is not recorded.
This is fitted with a Zeiss-Tessar lens of 2-inch focus.
In the Marey Institute investigations with the convolvulus, which was placed on a chair a short distance from the lens of the camera, sixteen successive snap-shots were made in the hour.
This, when it is extended and when the camera is fixed, brings the lens some 7 feet above the ground.
The missing parts of the motion--the parts lost while the lens is closed between the taking of each two pictures--are not detected by the eye.
The handle is revolved until the lens is opened, and the image thrown upon the matt film becomes apparent.
During the eclipse of the lens the spokes move more than the angle (AB) between them, and accordingly the wheel is seen to be moving naturally.
The camera is then placed overhead with thelens pointing downwards upon the centre of the title space.
The film is brought into position before the lensby passing through what is known as the "gate.
It is superior in the first respect because a lens transmits more light than a mirror reflects.
In the first place, a lens with spherical surfaces does not bend all the rays that pass through it to a focus at precisely the same distance.
In an analogous way the spherical aberration of a lens can be corrected by altering its curves, but the second difficulty that arises with a lens is not so easily disposed of: this is what is called chromatic aberration.
For practical use an eyepiece composed of an ordinary single lens is seldom advantageous, because good definition can only be obtained in the center of the field.
We thus learn that the distance of the image from the lens varies with the distance of the object whose image is formed.
Hold the reading glass between the eye and a distant object with one hand, and with the other hand place a smaller lens such as a pocket magnifier, near the eye, and in line with the reading glass.
With such a lensthe magnifying power of the telescope is measured by the ratio of the focal length of the objective to that of the eye lens.
The chromatic combination consists of a convex lens of crown backed by a concave, or plano-concave, lens of flint.
The rays that pass near the outer edge of the lens have a shorter focus than that of the rays which pass near the center of the lens; this is called spherical aberration.
The Dean drew instantly from his pocket the bit of cotton cloth which we had tried to light with the lens the day before, and thrust it in my hand.
Why,' replied he, 'you told me something about people making fire with a lens made of glass.
