348 



SCIENCE. 



[N. S. Vol. lY. No. 89. 



red Rays of Great Wave-length : By Eknest 



F. Nichols. 



In the absence of the author this paper 

 was presented in abstract by Prof. E. L. 

 Mchols. The author has investigated the 

 optical (?) properties of quartz for waves 

 greater than 4 ji. 



The reflection from a surface cut perpen- 

 dicular to the optic axis was found to de- 

 crease steadily from 3|- % at wave-length, 

 4.5 /x to a minimum of 0.29 % at 7.4 //.. 

 From this point the reflection increases 

 rapidly to 14 % at 8 /^., 36 % at 8.1 ij., reach- 

 ing a maximum of 76 % at 8.4 /.*. A second 

 minimum of 51 % was found at 8.6 ij. and a 

 second maximum of 65% at 8.8 a^; beyond 

 which the reflection falls to 50 % at 9 /a. 



The transmission through a quartz plate 

 18^1 in thickness cut perpendicular to the 

 optic axis shows three pronounced mini- 

 mum and four maximum values between 

 4 [JL and 7 fi. The last maximum is at 7 //-. 

 The transmission at this point is 80 % 

 From this point the transmission falls to 

 51 % at 7.6 a, 36 % at 1 ,1 ij., 12 % at 7.9 m 

 and to a value less than 1% at 8.1 /i. Be- 

 yond 8.1 IJ. the transmission is imperceptible. 



A computation of the indices of refraction 

 from observed reflection and transmissions 

 by the Cauchy formula has given results 

 which agree with the Ketteler-Helmholtz 

 dispersion formula, which, according to 

 Bubens' constants, requires rays in the 

 region of 8 /z to be bent towards the apex 

 rather than towards the base of a quartz 

 prism. 



The reflection and transmission measure- 

 ments were made with a Torsion Eadi- 

 ometer. The radiations pass through a 

 fluorite window into a vacuum chamber, 

 and fall upon a blackened vane of mica, 

 2x15 mm., which is carried by a light arm 

 at a distance of 2 mm. to one side of a 

 quartz fibre. The deflection of the vane is 

 observed by means of a mirror, telescope 

 and scale. The sensitiveness of the instru- 



ment, with a full vibration period of 12 

 seconds, was such that the rays from a 

 candle at a distance of six meters gave a 

 deflection of 61 divisions on a scale distant 

 1 meter from the instrument. When prop- 

 erly protected the instrument is absolutely 

 without ' drift,' and the zero point remains 

 constant within a centimeter for days at a 

 time. 



An Experimental Study of the Charging and 

 Discharging of Condensers : By F. E. 



MiLLIS. 



In the absence of the author this paper 

 was presented by Ernest Merritt, who ex- 

 hibited a number of very fine photographic 

 tracings of alternate current curves and of 

 curves obtained by the charge and dis- 

 charge of condensers. The instrument 

 used was essentially a tangent galvanom- 

 eter with a miscroscopic soft iron magnet 

 and mirror placed in an intense magnetic 

 field and having about 17,000 free half-vi- 

 brations per second. 



Notes on certain Physical Difficulties in the Con- 

 struction of Modern Large Guns: By W. 

 LeConte Stevens. 



The author related some experiences in 

 connection with the manufacture of a large 

 gun at the Watervliet arsenal, on the Hud- 

 son river. 



On the Photographic Trace of the Curves de- 

 scribed by the Gyroscopic Pendulum : By 

 Ernest Merritt. 



The author exhibited a number of the 

 curves. 



On the Distribution of High Frequency Alter- 

 nating Currents throughout the Cross-Section 

 of a Wire : By Ernest Merritt. 

 The author exhibited, by platted curves, 

 the results of extensive calculations from 

 the formulae of Lord Kelvin and Heaviside. 



On the Compactness of a Beam of Light : By 



Ernest E. von Nardroff. 



The author calls the solid angle subtended 

 by the extreme rays of a beam of light at a 



