ADAMS. — TRANSMISSION OF RONTGEN RAYS. G73 



(5) The nature of the effect which occurs within the substance of the 

 sheet. 



Most of these subjects had ah-eady been investigated by various 

 observers at more or less length, by means of the photographic plate, 

 the Huoroscope, and ionization plieuomena ; but in view of the semi- 

 qualitative nature of photographic and fluoroscopic work, and con- 

 sidering the difficulty of an exact interpretation of the phenomena of 

 ionization, it seemed desirable to reinvestigate the subjects with a 

 strictly quantitative instrument. 



The results obtained confirm the work of earlier investigators in most 

 cases, but in one or two important particulars they are at variance with 

 generally accepted views. It is believed that such measurements as 

 those here published are valuable not only in themselves, but as an in- 

 dication of the way to a more accurate quantitative examination of the 

 nature of the Kontgen radiation than has yet been made, 



11. Apparatus. 



Figure 1 illustrates the suspended system of the instrument. It 

 consisted of a loop, L, of copper wire 0.026 cm. in diameter, completed 

 at the lower end by a bit of constantan wire, C, and a thin circular 

 piece of platinum, D. The junctions were made with a soft solder, no 

 acid being used, and all superfluous solder being removed. The wires 

 at the upper end of the loop were twisted together, and carried a light 

 mirror, M. A vertical section through the wooden case of the instrument 

 is shown in Figure 2. The loop of copper was hung by a fine quartz 

 fibre in a magnetic field due to the permanent magnets, N, S. The 

 block of soft iron, I, was drilled horizontally and vertically as repre- 

 sented, and was designed to prevent the magnetic field from exerting 

 a directive force on the suspended system. A copper sheathing, not 

 shown in the section, lined the central cavity of the wooden case 

 throughout its length. The Runtgen rays entered the instrument 

 through a thin aluminium window at A and were partially absorbed 

 in the platinum. The heat thus developed at the lower junction of 

 the copper-constantan couple produced an electric current around the 

 loop, which caused the suspended system to rotate in the magnetic 

 field until brought to rest by the opposing toreion of the fibre. The 

 dimensions of the instrument may be estimated from Figure 2, which 

 is about one third actual size. The thickness of the absorbing platinum 

 was 0.0014 cm., and its diameter 0..S8 cm. The thickness of the 

 aluminium window was 0.015 cm. A telescope and scale, the latter 

 151 cm. from the mirror, were used to read the deflections. 



Disturbances of many sorts were encountered and, so far as possible, 



VOL. XLII. 43 



