Fkbbuakt 15, 1918] 



SCIENCE 



171 



came very bright and complete except for the 

 portion below the horizon. It clearly showed 

 red on the inside and blue on the outside. 

 Tangent to this halo, directly above the Bxtn 

 and convex toward it, was a strongly colored 

 arc of a circle, red on the convex and blue on 

 the concave side. 



As the Sim's altitude increased the parhelic 

 circle gradually extended until it reached 

 nearly around the horizon and the paran- 

 thelia 120° from the sun had become very 

 distinct patches of white light. The 22° par- 

 helia meanwhile had become dazzlingly bright, 

 considerably elongated perpendicularly, and 

 showed orange red on the side farthest from 

 the sun. This color arrangement being the 

 reverse of that of the 22° halo seems peculiar. 



The phenomena remained visible until about 

 eleven o'clock before which time the 22° halo 

 appeared as a complete circle above the horizon 

 and the parhelion directly below the sun 

 showed brightly. Before vanishing the bright 

 46° halo and its brilliantly colored tangent 

 arc appeared almost at the zenith. 



Measurements of the diameters of the halos 

 and the angular positions of the parhelia were 

 made with an improvised transit. No claim 

 to accuracy can be made for them, both be- 

 cause of the apparatus and because of the 

 bright and diffuse nature of the objects, but 

 the results obtained are practically those given 

 above as was to be expected. 



The temperature during the night had been 

 below zero and in the morning was still 3° or 

 4° below it. The air was quiet and filled 

 with falling crystals of ice. 



0. C. Lester 



Universitt or Color.u)o 



MARKING MICROSCOPE SLIDES 



In the issue of Science for January 4, Mr. 

 P. A. West gives an aluminum clip method 

 for labelling glass slides while staining which 

 he finds more satisfactory than the diamond 

 pencil or the water-proof-ink method. 



With me his objection to a label scratched 

 on the glass does not hold, as I use a jar in 

 which the upper end of the slide is not covered 

 by the stain. I have for several years used 



an improvised carborundum pencil and have 

 found it most satisfactory. 



A fair-sized crystal of carborundum, chosen 

 for one or more sharp points is laid between 

 the two halves of a firm piece of elder pith 

 about an inch and a half long, with the sharp 

 end projecting only sufficiently to make its 

 use easy. Rubber bands are then wound 

 tightly about both ends of the pith, holding 

 the carborimdum firmly in place. The pencil 

 may be pointed up by trimming the edges of 

 the pith aroimd the crystal. This pencil is 

 more easily handled than the bare crystal and 

 scratches the data quickly and easily on the 

 slides. 



Mary K. Bryan 



Department op Agricttlture 



SCIENTIFIC BOOKS 



The Organization of Thought. By A. N. 

 WH1TEHE.U), Sc.D., F.R.S., Fellow of Trin- 

 ity College, Cambridge, and Professor of 

 Applied Mathematics at the Imperial Col- 

 lege of Science and Technology. London, 

 Williams and Norgate. 1917. Pp. 219. 

 This volimie is a collection of eight dis- 

 courses bearing the following titles: 



I. The Aims of Education — A Plea for Eef orm. 

 II. Technical Education and Its Relation to Sci- 

 ence and Literature. 



III. A Polytechnic in War-time. 



IV. The Mathematical Curriculum. 



V. The Principles of Mathematics in Relation 

 to Elementary Teaching. 

 VI. The Organization of Thought. 

 VII. The Anatomy of Some Scientific Ideas. 

 VIII. Space, Time and Relativity. 



Except number VII., which is here pub- 

 lished for the first time, the articles are ad- 

 dresses delivered before various scientific as- 

 sociations in course of the last four years. 

 The range of discussion is wide, even wider 

 than the diversity of titles might lead one to 

 expect; yet the discussions have a deep unity 

 in the fact that they deal with various aspects 

 of one great matter, the organization of 

 thought, and so the book is happily named. 

 Fresh, direct, trenchant, vital and swift, the 

 style is such as to give the reader more energy 



