1Y6 O. N. Rood — Reflection of the Rontgen Rays. 



0-264°'°'. The angle as before was 45° ; the total distance 

 from the discharge tube to the sensitive plate was lYY™"". The 

 exposure lasted fifty hours and a strong negative was obtained. 

 Just as in the previous experiment, a comparison negative was 

 taken in a dark room with the ordinary light furnished by the 

 tube and reflected from the mirror, the plate as before being 

 naked and covered only by the netting. The exposure in this 

 case lasted two minutes, though subsequent experiments 

 showed that thirty seconds would have answered. Although 

 the speculum mirror sent regularly reflected ordinary light to 

 only one-half of the naked plate, yet the ordinary light diffused 

 from its surface acted on the whole of the plate and gave a 

 strong negative, which of course was much denser in that half 

 of the plate reached by the regularly reflected rays. 



It having thus been proved that the speculum mirror sent a 

 portion of diffused ordinary light to the half of the plate not 

 reached by regularly reflected light, it was to be expected that 

 the same result would follow in the case of the plate exposed 

 to the X-rays. This was found to be the case, but the differ- 

 ence in the densities of the two halves of the negative was less 

 well marked. In the case of the X-ray negative, the vertical 

 lines were somewhat blurred and broadened, owing to the 

 action of the diffused rays, but in most portions of the plate the 

 horizontal lines were sharp and not sensibly broader than the 

 wires of the netting. This fact is difficult to account for on 

 the supposition that the speculum mirror sent to the plate 

 only diffused X-rays, as will be seen by what immediately 

 follows. In order to ascertain what kind of an image diffused 

 ordinary light, unmixed with regularly reflected light, would 

 furnish, the face of the mirror was neatly covered with white 

 paper which had been chalked to remove the last trace of its 

 glaze. Negatives were taken in the same manner as that 

 employed with the comparison plates above mentioned, the 

 exposures being one, ten and thirty seconds. The three agreed • 

 in their details, but their appearance was totally different from 

 that of the X-ray negative, the horizontal lines in particular 

 being ^"^^ in breadth, instead of about 0-8™"", as was the case 

 with the X-ray negative. 



Experiment with a platinum mirror. — A piece of platinum 

 foil was now cut of the same shape and size as the speculum 

 mirror, and put in the position previously occupied by the 

 latter. The platinum was cemented on a plate of glass having 

 a plane surface, pains being taken to make the platinum lie as 

 flat as possible. Its polish was not bad, but in spite of all 

 efforts it was impossible to remove its small but visible irregu- 

 larities of surface. As was to be expected, when used as a 

 looking glass it furnished an image which was not distorted, 



