544 Drs. J. T. Bottomley and J. C. Beattie on 



of the radiation from surfaces of various kinds in high 

 vacuum. 



When a body is maintained at a high temperature the total 

 radiation from its surface depends, other things being the 

 same, on the temperature and on the character of the radiating 

 surface. With a given temperature the total radiation, con- 

 sisting of thermal, luminous, and actinic rays, seems to depend 

 on the nature and on the ultimate texture of the radiating 

 surface; and the proportion in which vibrations of longer and 

 shorter period are present seems to be governed by the 

 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 inves- 

 tigation 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 Schleiermacher f has compared the loss from bright 

 platinum wires and from platinum wires whose surface was 

 coated thinly with black oxide of copper. Further experi- 

 ments 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 J. The pla- 

 tinum wire, a b, is held, stretched between two spiral springs, 

 in a glass tube. The outer ends of the spiral springs termi- 

 nate in loops; and two pieces of glass rod, which are passed 

 into tubes c c, d d (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, d d are 

 closed up, except one, which is used for exhausting. Flexible 

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

 are sil\er-soldered to stout multiple platinum terminals; and 

 by means of these, which are fused, with the help of some 

 white enamel, into the glass at d, d, the current is passed 

 through the platinum wire. At e, e platinum wires are 

 brought through the sides of the tube, and serve as potential 

 electrodes ; and it is to keep the platinum wire a b in the 

 middle of the length of the tube, and to avoid pulling unduly 

 on the potential electrodes, that the two spiral springs, one 

 at either end of the tube, are introduced. 



* Bottomley, Roy. Soc. Prec. ]887. 

 f Schleiermacher, Wied. Ann. vol. xxvi. 1885. 



X The arrangement has heen already described, J. T. Bottomley, Phil. 

 Trans, vol. clxxviii. A, p. 448 (1887). 



