218 Scientific Intelligence. 



dC 2b s 



31-3 X 1*59 X 0-022 cm , it was found that ~pp = 0'0256, -^=0-0214, 



Qj -L Ob 



C = 308 500, and n = 8'555 X 10". "In the strip 0*01 cm thick 

 the restoring couple under the greatest tension is 48*5 per cent 

 above that under least tension: this shows the necessity of allow- 

 ing for the bifilar effect when obtaining the rigidity of materials 

 by experiments with strips." It is thus seen that, in general, the 

 complete formula gives very satisfactory results. The outstand- 

 ing anomalies found by other observers may be accounted for as 

 due to overstraining the materials employed. — Phil. Mag., xxviii, 

 p. 778, December 1914. h. s. it. 



8. Volatility of Thorium D. — The behavior of thorium D 

 at different temperatures and when treated with nitric acid and 

 hydrochloric acid has been recently studied in detail by A. B. 

 Wood. The forms of the electric furnace and /3-ray electroscope 

 are not novel and hence a description of the apparatus would be 

 superfluous in this place. The results obtained may be briefly 

 summarized as follows : The temperature of volatilization of tho- 

 rium D was found to be 520° C, both when this element had not 

 been treated with acid and when it had been dissolved in pure 

 nitric acid. On the other hand, when thorium D had been treated 

 with hydrochloric acid the temperature of volatilization assumed 

 the much lower value 270° C. The views of earlier investigators 

 concerning the formation of definite chemical compounds of the 

 active deposits of the various radio-active elements are confirmed 

 by the work of Wood. This investigator also found that thorium 

 D recoils from thorium C in the atomic form, irrespective of 

 whether the parent thorium C was free or combined with acids. 

 Finally, in the case of thorium D recoiling from the active deposit 

 of thorium dissolved in hydrochloric acid, evidence was obtained 

 that a portion of the recoiling atoms recombine with the free 

 chlorine which is liberated when the molecules of thorium chlor- 

 ide disintegrate. — Phil. Mag., xxviii, p. 808, December, 1914. 



h. s. u. 



9. Lecture Experiment on Dispersion. — The following brief 

 account of the experimental demonstration of the irrationality of 

 dispersion is taken from a paper by Silvanus P. Thompson. 

 Light from an electric arc is focussed on a small round or square 

 hole in an opaque diaphragm and a horizontal spectrum of this 

 source is projected on the screen or wall by means of a diffraction 

 grating having about 12,000 lines to the inch. "On interposing 

 a prism to disperse the light vertically upwards, the resultant 

 oblique spectrum is finely curved, being concave upwards." The 

 curvature observed is due to the irrationality of dispersion of the 

 particular prism employed, since for all known kinds of glass the 

 refrangibility of the blue and violet waves is disproportionately 

 large. The demonstration is enhanced either by using the car- 

 bons supplied for commercial "flame arcs" or by tamping an 

 alloy of lithium, thallium, and zinc in the positive carbon. This 

 scheme is obviously preferable to Newton's method of crossed 



