Page:Popular Science Monthly Volume 91.djvu/139

 Using a Drop of Water for a Lens

It Is a wonderful magnifier in microscopic photography By Frank M. Gentry

��EVERY amateur photographer will be glad to learn of a method that is both simple and inexpensive, by which he may make perfectly clear photographs of microscopic objects.

It has been known ever since the first scien- tific investigations of the refractive properties of different substances, that water, if it could in some practical way be held in shape, would form a lens of extraordinary value. Moreover, it is also well known that a drop of water held by capillary attraction in a loop of wire forms a wonderful magnifying lens. The question,

therefore, arises, "Why not use this drop of water as a photographic lens?" An explanation of how this might be done follows:

The first step is to cut a disk A from very thin copper to fit the lens cell of the camera. In the center of this disk, B, there should be bored a 1/32-in. or smaller hole. The smaller the hole is, the more perfect the lens will be and, therefore, the greater its work- ing capacity. The edges of the hole should

���The camera as it is mounted on a pedestal for microscopic photography

��as to remove all the little particles of pro- jecting copper. Great care should be taken to follow accurately these instruc- tions, as the result will depend on your faithfulness in this re- spect.

Next remove the lens from its cell ; reverse the threaded ring which held it in place; insert the copper disk, and screw in place with the ring. The result may be seen in the illustration on page 125, where C rep- resents the lens cell; D, the threaded ring; E, the copper disk, and F, the drop of water. The cell may now be screwed back into the camera until ready for use.

In order to place a drop of water in the hole, a wire should be bent as shown at G. Dip the straight end into the water. When it is re- moved, the drop that adheres will be just enough to properly fill the opening. Patience is required to place the drop accurately so that it will not run over the edges, which would be disastrous. The operation may consume over an hour but the results well atone for the trouble.

��then be rubbed carefully on an oilstone so Glycerine or castor oil may be used in place

���At left: Crystalline formation of a bichromate of potassium solution on a gelatine slide. In center: Portions of the antennae of a beetle. At right: Microtomic cross-section <>f a stem of fern

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