270 Drs. J. T. Bottomley and J. C. Beattie. 



coarseness or fineness of the structure of the surface at which the rays 

 take their origin. 



Very little progress has yet been made towards an investigation of 

 the question just referred to ; and the results of our experiments are 

 intended to be a contribution in this direction. 



In a former paper* by one of us the loss of heat in vacuum from the 

 metallic surface of platinum wires was determined ; and Schleiermacherf 

 has compared the loss from bright platinum wires and from platinum 

 wires whose surface was coated thinly with black oxide of copper. 

 Further experiments on this part of the subject seemed highly desirable, 

 and were, therefore, undertaken by us. 



The radiating body was a platinum wire. The way in which it was 

 mounted is shown in figs. 1 and 2.| The platinum wire, ab, is held, 



Fig. 2. 



stretched between two spiral springs, in a glass tube. The outer ends 

 of the spiral springs terminate in loops ; and two pieces of glass rod, 

 which are passed into tubes, cc, c'c (see figure), pass through the loops, 

 so that the springs pull on these glass rods. After the rods have been 

 passed into their places, the ends of the tubes cc, c'c' are closed up, 

 except one, which is used for exhausting. Flexible electrodes are 

 soldered to the loops of the spiral springs, and are silver soldered to 



* Bottomley, ' Koy. Soc. Proc ,' 1887. 



t Schleiermacher, ' Wiedemann Annalen,' vol. 26, 1885. 



X The arrangement has been already described, J. T. Bottomley, 'Phil, Trans,,' 

 A, 1887, vol. 178, p. 448 



