470 A. M. Mayer — Researches on the Rontgen Rays. 



number differs greatly from that of Herapath, I thought that 

 the small mass I had used was the cause of the discrepancy. 

 I then made about two grams of herapathite, freed it of its 

 mother liquid by washing with water at 0°, and dried it at 25° 

 in vacuo. When it had ceased to lose weight I weighed it in 

 a specific gravity flask holding about 10 c.c., then just covered 

 it with water, placed it in vacuo and agitated it, so that it 

 would be freed of any air that might be contained in its mass. 

 The flask was then nearly filled with water and again placed in 

 vacuo, then entirely filled and weighed. I found from this 

 carefully made experiment that the density of herapathite is 

 1-557 at 20° C. 



8. The formulce of transmission of the Rontgen rays through 

 glass, aluminum, platinum, green tourmaline and herapathite. 



The Rontgen rays, after their transmission through various 

 substances, produce actinism on a photographic plate, and by 

 the degree of this actinism we have attempted to obtain the 

 formula of transmission peculiar to each substance. This 

 action of the X-rays is cumulative and evidently is entirely 

 different from the transmission of light and radiant heat where 

 the maximum of transmission is instantly reached and under 

 proper and controllable conditions remains constant and there- 

 fore can be accurately measured. But with the X-rays the 

 amount of their action on the plate varies directly as the time 

 of their action (see 4), depends on the distance of the sensitive 

 plate from source of radiation, and on the energy of the source. 

 Therefore this* method of determining the constants of the 

 formulae of transmission of the X-rays is somewhat arbitrary ; 

 but the exact conditions in the determination of the constants 

 having been given, these conditions can readily be obtained by 

 other experimenters. Thus, to have the same conditions as 

 existed in our experiments, one has only to place a pile of 

 crown glass plates 5'5 mm thick, at such a distance from the 

 radiant source that on two hours exposure the X-rays will have 

 just not visibly acted on the photographic plate. Some assump- 

 tion has to be made as to the nature of the X-rays, otherwise 

 no progress can be made in determining the constants of their 

 formulae of transmission. We have assumed that they are 

 homogeneous. The formulae, as determined, hold good till 

 they have conclusively been shown not to be homogeneous, 

 which is very likely to happen in the progress of research on 

 their nature. 



The method used owes whatever merit it may have to the 

 use of the wire netting devised by Professor Eood to give 

 accurate indications of the relative permeability of various 



