180 



SCIENCE. 



[N. S. Vol. XVI. No. 396. 



On the Formation of Deiu Botvs: Lyman 



J. Bbiggs, Wasliington, D. C. 



A description was given of the formation 

 of a prismatic bow caused by the reflection 

 and refraction of light from drops of dew 

 supported on extremely fine spears of grass. 



Note on a New Form of Laboratory Sivitch- 

 hoard Jack: F. C. Caldwell, Univer- 

 sity of Ohio. 



This form of jack, which has proved very 

 successful, is made up of one or more brass 

 tubes with a shoulder at one end and 

 threaded at the other, so that an ordinaiy 

 nut screwed on will hold the jack in the 

 board. Where opportunity for inserting 

 two or more plugs is required, these jack 

 tubes are united by yokes on the back of 

 the board. Ten of these jacks after several 

 months' use averaged six-thousandths- volt 

 drop when carrying 100 amperes. The 

 plug for this jack is a straight piece of 

 three-eighths-inch rod slit at the end and 

 fastened in a handle. The cost of such a 

 single jack with nut, washer and plug com- 

 plete is trifling. 



Note on a New Variable Ironless Induction 



Coil for Large Currents: F. C. Cald- 



v\^LL, University of Ohio. 



This coil is interesting because of its 



large size. It is made up of two concentric 



coils, one swinging within the other. Its 



resistance is 1.4 ohms, and its impedance, 



with sixty period current, about forty olims. 



It is wound with ten layers of twenty turns 



of No. 8 wire in the outside coil, and nine 



layers of twenty turns in the inside layer. 



About one hundred pounds of wire was 



used in the construction. The outside 



diameter of inside coil is twenty inches. 



On ilolecidar Friction in Steel and Phos- 

 phor-Bronze: J. 0. Eeed, University of 

 Michigan. 

 The method consisted in observing the 



time required for a tuning fork to diminish 



its amplitude of vibration from one fixed 

 amplitude to another, the tuning fork being 

 enclosed in a chamber heated electrically, 

 and the amplitudes being observed by a 

 telescope. This period of time becomes a 

 minimum at about 70°C. and then increases 

 again. The diminution in amplitude was 

 assumed to be due chiefly to molecular fric- 

 tion. 



Young's Moduhis for Phosphor-Bronze, 

 Between 20° and 300° C: J. 0. Reed, 

 University of Michigan. 

 The phosphor-bronze was in the form of 

 the tuning fork of the last paper and it was 

 heated in the same chamber. The paper 

 described the additional appliances neces- 

 sary to measure Young's modulus. The 

 results obtained were given. 



A Photographic Study of the Alternating 

 Arc: G. A. Hoadley, Swarthmore Col- 

 lege. 



An alternating arc was observed . under 

 the following conditions: (a) Between car- 

 bon points, ordinary; (5) between carbon 

 and zinc points, showing that there is an 

 illuminating arc only once per cycle, and 

 that there is a direct current passing from 

 zinc to carbon in the arc, which can be read 

 by a direct-current ammeter; (c) between 

 carbon points in a magnetic field showing 

 the alternating direction of the current; 

 (d) between carbon points, the lower of 

 which is double, showing that two direct- 

 current ammeters placed in the lower 

 branches will show two direct currents if 

 placed in opposite directions. 

 The Nernst Lam^p: A. J. Wurts, Pitts- 

 burgh, Pa. 



Mr. AVurts gave a very interesting ac- 

 count of the technical evolution of the 

 Nernst lamp in this country, mentioning 

 many of the defects in the original which 

 had been overcome by the ingenuity of 

 American engineers. The lamp in its pres- 



