A STUDY OF SNOW CRYSTALS. 77 



The illustrations which accompany this article are all of them 

 photomicrographs taken directly from crystals which were collected 

 in northern Vermont during the past fifteen years. They are se- 

 lected from over five hundred different forms. A close and minute 

 study of many of them will reveal beauty and complexity of struc- 

 ture not seen by a casual observer. The methods employed in 

 obtaining the illustrations have been very simple. It has been 

 found that any apparatus which can be used for taking photomicro- 

 graphs will serve to photograph snow crystals, but the microscope 

 should be fitted with half-inch or two-thirds-inch objectives, of wide 

 aperture and short axis; the focusing arrangement must work 

 (juickly and accurately; the diaphragm aperture be small, not more 

 than one-sixteenth inch; the illumination ordinary, uncondensed 

 daylight; the exposure, rapid plates being used, from forty seconds 

 to three hundred, as the light is strong or weak, camera bellows 

 closed or elongated, etc. A black card placed between two pins 

 which project from the stage on each side of the objective serves to 

 exclude unwelcome light when the slides of the plate-holder are 

 changed. Great care is necessary to prevent the crystals from melt- 

 ing, as this is one of the chief difficulties which must be overcome. 

 On this account the observer must not breathe upon his slides, nor 

 liandle them except with gloved hands. The whole work must be 

 done in a cold room, with but one unscreened window. Crystals may 

 be collected as they fall, upon a black card, and transferred by a 

 bit of broom splint to a glass slide upon which they may be pressed 

 flat with a feather. 



Careful examination of the illustrations will soon convince one 

 that, great as is the charm of outline, the internal ornamentation of 

 snow crystals is far more wonderful and varied. Many of the speci- 

 mens, we might almost say all of them, exhibit in their interior most 

 fascinating arrangements of loops, lines, dots, and other figures in 

 endless variety. So far as is known to the writer, these illustrations 

 are the first which have been published that show in any adequate 

 manner these interior figures, and surely they add greatly to our in- 

 terest and delight as we study snow crystals. So varied are these 

 figures that, although it is not difficult to find two or more crystals 

 which are nearly if not quite the same in outline, it is almost impos- 

 sible to find two which correspond exactly in their interior figures. 



It is asserted by some obser^^ers that many of the lines or rods 

 seen in the interior of snow crystals are really tubes filled with air. 



Perfect crystals are by no means always common in snow storms, 

 most of the forms produced being more or less unsymmetrical or 

 otherwise imperfect. It rarely happens that during a single winter 

 there are more than a dozen good opportunities for securing com- 



