FRAGMENTS OF SCIENCE. 



719 



ure. ... In some cases the system has been 

 adopted sparingly and timidly, as if under 

 stress of competition. More often it has 

 been received heartily up to a certain limit." 

 The method of its application has, however, 

 been very diversified, resulting in a great 

 variety of schemes, a considerable number 

 of which are reviewed and analyzed by the 

 author. " No two colleges agree as to what 

 studies are ' essential for all who are candi- 

 dates for a liberal degree.' As to the work- 

 ing of the elective plan, the author believes 

 that its risks are overestimated." No can- 

 did observer of college life can deny that 

 free choice has promoted vital scholarship 

 and hastened the growth of manly judgment 

 in college students. It has revolutionized 



college teaching by sealing the doom of the 

 lazy instructor. It has steadily extended its 

 conquests, and is pushing its way into more 

 colleges and over wider areas of the college 

 course. That it should stand without im- 

 portant checks few would contend, but that 

 the college student does not often abuse the 

 elective privilege is, in the belief of the 

 author, capable of proof. And a contribu- 

 tion to this proof is made from the records 

 of the author's own college, Colgate Univer- 

 sity. Professor Bingham regards his study, 

 as a whole, as indicating the sobriety, ear- 

 nestness, and intelligence of the college man, 

 and has no question that, " for the average 

 man, sound habits of steady endeavor grow 

 best in fields of choice." 



MINOR PARAGRAPHS. 



By availing himself of the properties of 

 surface tension, M. Charles Henry has dis- 

 covered a method of producing permanent 

 coloration by the use of light-colors, without 

 the aid of any pigment. Liquids having a 

 superficial tension less than that of water are 

 deposited on water in thin layers, where they 

 reflect the colors of the spectrum. By 

 whistling over this layer we obtain for each 

 tone a vibration which is responded to by a 

 special coloration, and a kind of molecular 

 landscape is produced. The liquid, how- 

 ever, soon evaporates, and the play of col- 

 ors vanishes. In order to preserve the col- 

 ors, a fixed excipient is introduced into the 

 liquid, which will retain the thickness of 

 the pellicular layer, and the colors as well, 

 after the essence has evaporated. Some 

 resin or coal-tar substance is used for this, 

 giving permanence to the pellicle and the 

 picture. M. Henry has further devised a 

 process for producing this pellicle and pic- 

 ture upon a solid foundation, as of wood, 

 glass, or paper, and even for accomplishing 

 it by mechanical processes. The nature of 

 the ground in which the picture-pellicle is 

 laid has much to do with its character. 

 Dark grounds give intense colors, white 

 grounds lighter ones, and grounds of inter- 

 mediate colors various shades. The process 

 is called iri chromatime. 



The images left by uranium upon a sen- 

 sitive plate locked up with it ip the dark 

 may be regarded as an effect of the fluores- 



cent property that metal is known to pos- 

 sess. Dr. Russell has, however, described 

 to the Royal Society experiments from 

 which it appears that mercury, zinc, mag- 

 nesium, cadmium, aluminum, nickel, pewter, 

 bismuth, lead, tin, antimony, and cobalt give 

 out radiations capable of affecting the sensi- 

 tive plate, and will leave images of them- 

 selves after standing upon one in the dark 

 for about a week, although they possess no 

 evident luminosity. Gold, platinum, and 

 iron exhibit little or no power of the kind. 

 A figure scratched upon the polished face of 

 a sheet of zinc repeated itself. The interpo- 

 sition of a coat of varnish between the metal 

 and the plate served to increase the effect, 

 while glass, which makes no difference 

 when uranium is applied, stopped the action 

 with the other metals. Some non-metallic 

 substances, such as straw, wood, charcoal, 

 and printer's ink, presented the same prop- 

 erty of leaving images. A section of young 

 larch wood printed its formation clearly on a 

 plate, so that the rings and bark could be 

 made out. In many cases the activity was 

 increased by heating the body, and dimin- 

 ished by cooling it. 



A siLiciFiED tree is described by Lewis 

 Woolman in the Report of the Geological 

 Survey of New Jersey which lies in the 

 orange-colored sand near Lindenwold in that 

 State. The farmer of the land having regu- 

 larly plowed up pieces of silicified wood, 

 Mr. Woolman and his friends dug for the 



