54 Mr. W. G. Gregory on a New 



preceding series of lunar researches was born by one of the 

 most generous and disinterested friends that Science has had 

 in this country, the late William Thaw, of Pittsburgh. By 

 his own wish, no mention of his name was made in previous 

 publications in connexion with the results so greatly indebted 

 to his aid. His recent death seems to remove the restriction 

 imposed by such a rare disinterestedness. 



IV. On a New Electric Radiation Meter. (Preliminary Note.) 

 By W. G. Gkegory, 31. A., Demonstrator in Physics at the 

 Royal Indian Engineering College, Coopers Hill*. 



THE usual method of detecting electric radiations by ob- 

 serving the sparking across an air-gap in the wire used as 

 a receiver admits of only a rough estimate of their intensity. 



The object of this paper is to describe an instrument by 

 means of which definite quantitative measurements may be 

 made. Jt is based on the measurement of the elongation of a 

 wire when heated by the currents induced in it by the rapidly 

 varying field of force. 



It consists of a long glass tube A B cemented to a shorter 

 piece of brass tubing B D. Within is stretched a platinum 

 wire W fastened to the glass tube at Aand to a Perry magnifying- 

 spring at M, where there is a mirror to indicate the rotation 

 of the spring by the reflexion of a beam of light upon a scale. 

 At E there is a nut and screw for adjusting the tension. The 

 brass tube is partially filed away in front of the mirror to 

 form a window. The object of the brass tube is to compensate 

 the spring for general changes of temperature, the glass tube 

 serving the same purpose for the platinum wire. 



The wire employed was '0086 cm. in diameter, and 192 cms. 

 long. The spring was about 25 cms. long and '007 cm. 

 in diameter. It was made out of a fine kind of tinsel *04 cm. 

 wide and '0015 cm. thick, which can be obtained at fancy shops 

 wound loosely on cotton. When removed from the cotton, it 

 was already in the form of an irregular helix. It was then 

 rolled tightly between the fingers to reduce the diameter as 

 much as possible. A piece of silk was next attached to one 

 end, and the spring extended almost to breaking-point, the 



* Communicated by the Physical Society : read November 1, 1889. 



