Intelligence and Miscellaneous Articles. 381 



structed my apparatus with the Rontgen tube projecting to- 

 one side, as shown in the side view, fig. 2. This makes a 

 support for the pump so that it will stand alone. A pump of 

 this description in connexion with an ordinary " Dark-space - " 

 tube makes a very convenient piece of lecture-room apparatus 

 for showing the character of the discharge at different pres- 

 sures. By tipping the pump far enough the upper trap can 

 be emptied, and the air stored in B returned to the discharge- 

 tube again, showing the phenomena at higher pressure. 



Owing to the absence of rubber connexions and stopcocks, 

 the mercury remains always clean and there is no leakage. 



I am now constructing a pump on this principle on a large 

 scale for general laboratory use in which the rocking motion 

 is to be effected by water-pressure, which, if found serviceable, 

 will be described in a subsequent paper. The chief objection, 

 of course, is that the entire pump is in motion, which makes 

 its connexion with a stationary receiver somewhat difficult. 

 This can perhaps be done by bringing the exhaust-tube into 

 coincidence with the axis of rotation, and using a rubber tube 

 surrounded with mercury as a joint. 



The small pump can be ordered with or without the 

 Rontgen tube from Herr Glasblaser R. Burger, Chaussee- 

 str. 2 E, Berlin, Germany. 



Berlin : Physikalische Institut. 



XL. Intelligence and Miscellaneous Articles. 



NOTES OF OBSERVATIONS ON THE RONTGEN RAYS. 

 BY HENRY A. ROWLAND, N. R. CARMICHAEL, AND L. J. BRIGGS. 



rPHE discovery of Hertz some years since that the cathode rays 

 -*- penetrated some opaque bodies like alaminium, has opened up a 

 wonderful field of research, which has now culminated in the 

 discovery by Rontgen of still other rays having even more 

 remarkable properties. We have confirmed, in many respects, 

 the researches of the latter on these rays and have repeated his 

 experiments in photographing through wood, aluminium, card- 

 board, hard rubber, and even the larger part of a millimetre of 

 sheet copper. 



Some of these photographs have been indistinct, indicating a 

 source ol ! these rays of considerable extent, while others have been 

 so sharp and clear cut that the shadow of a coin at the distance 

 of 2 cm from the photographic plate has no penumbra whatever, but 

 appears perfectly sharp even with a low-power microscope. 



So far as yet observed the rays proceed in straight lines, and all 

 efforts to deflect them by a strong magnet either within or without 

 the tube have failed. Likewise prisms of wood and vulcanite have 



Phil. Mag. S. 5. Vol. 41. No. 251. April 1896. 2 D 



