120 



SCIENCE 



[N. S. Vol. XLIX. No. 1257 



bubbles. Tlie formation of the caps that 

 finisbed off tlie completed, or dead, columns 

 is, perhaps, to be explained in this way : When 

 the column rose to a point where the wind 

 reached it above the lee of the dam, the spray 

 from the bursting bubbles would lodge chiefly 

 on the leeward, or downstream, side of the 

 orifice and in freezing would build up that 

 side faster than the upstream side. The top 

 would thus curve over upstream, the freezing 

 spray building not only upwards but back 

 against the wind, just as the hoar-frost or 

 frozen mist of mountain-tops builds against a 

 high wind. This would, of course, close the 

 orifice in time and put a stop to the growth of 

 the column. 



It is not entirely clear how the bubbles rise 

 to so considerable a height in the tubes — 

 whether they are forced up by the rush of 

 water over the dam and under the hood of 

 ice, or whether it is because the air they con- 

 tain is heated by the water to a higher tem- 

 perature than the surrounding air. On this 

 point, as on the whole subject, we should be 

 very glad to get the opinions and observations 

 of any one else who has seen this formation. 

 Inquiry among friends has failed as yet to 

 bring to light any similar observations on the 

 part of others, and we find no mention of this 

 phenomenon in the fourteen volumes of 

 Thoreau's " Journal," observant as he was of 

 the forms taken by ice, snow and frost along 

 the Concord River and its tributaries. This 

 has made otu- observation seem worth record- 

 ing, though we can not doubt that under sim- 

 ilar circumstances it might be repeated any 

 cold winter. 



Frederick A. Lo'S'ejoy, 

 Francis H. Allen 



West Eoxbubt, Mass. 



CELLULOID LANTERN SLIDES 



To THE Editor of Science : In a recent letter 

 to Science regarding celluloid lantern slides, 

 Mr. A. W. Gray states that " tracing cloth and 

 waxed paper are usable ; although their limited 

 transparency produces a rather dark field, and 

 the texture of the material shows plainly." 

 The writer experimented some time ago with 



substitutes for glass lantern slides, giving spe- 

 cial attention to slides which could be prepared 

 quickly for temporary use. 



I found that a satisfactory slide could be 

 made by drawing figures or diagrams on thin 

 white paper with India or colored ink. After 

 the ink had become thoroughly dry both sides 

 of the paper were brushed over with a light- 

 colored penetrating oil. The thin glazed white 

 paper used for duplicating typewritten letters . 

 serves admirably for the paper and a light 

 neatsfoot makes a satisfactory oil. These paper 

 slides may be inserted in cardboard holders and 

 with suitable projecting apparatus the results 

 are all that could be desired. 



The eifect of the oil is to increase greatly the 

 transparency of the paper and when new the 

 texture of the paper is quite imperceptible. 

 Figures of lesser sharpness can be made with a 

 fountain pen or even with a pencil. Diagrams 

 and pictures of appropriate size may be cut 

 from magazines or bulletins and treated with 

 oil as outlined above. These are more satis- 

 factory, of course, if no printing appears on 

 the back, but for temporary use the printing 

 in many cases will not destroy the usefulness 

 of a diagram. 



I have also made good slides in the same 

 manner by treating 3i X4J photographic 

 prints with oil. The projected pictures, while 

 less bright than those procured with glass 

 plates, present a softer efiect and are especially 

 interesting in the case of portraits. Since the 

 usual photographic paper is quite heavy the 

 lantern must be placed nearer the screen but 

 if thinner paper could be obtained the results 

 >vould be quite satisfactory if the usual dis- 

 tance were maintained. 



Ealph G. Hudson 



Department op Physics, 

 Kenton College 



holding large specimens for dissection 

 In the zoological laboratory there are many 

 things which are valuable aids in time and 

 convenience. In dissecting large specimens it 

 is often necessary to have some method of 

 holding parts of the anatomy away so as to 

 allow freer rein to one's actions, or of holding 



