Page:Proceedings of the Royal Society of London Vol 69.djvu/59

Rh Line.

Scale.

Wave-length.

Old.

New.

D

50-0 39-3 46-8 81-8 30-5 109-0 41-2 73-0 92-8 64-1 64-4 64-5 81-6 56-5 57-5 37-1 56-3 98-3

17-7 7-0 14-5 49-5 1-8 76-7 8-9 40-7 59-5 31-8 32-1 32-2 49-3 24-2 25-2 4-8 24-0 66-3

5889 6708 6102 4603 7680 4045 6563 4860 4340 5183 5172 5167 4607 5535 5492 6933 5543 4226

K, red

H, C

H, F ..

H

Ms. green.

Sr blue

Ba

Ba

Ca

Ca. .

Ca

The D line on the new scale was at 17 '7, and as it was also a milli- metre scale, the new scale readings will all be 32*3 less than the previous ones.

To test this the following readings were taken :

Stem.

D.

Li, red.

Li, blue.

Mg.

Old scale

50-0

39-3

81-8

64-5

New scale

17'7

7-8*

49-5

32-3

Difference

32-3

31-4

32-3

32-2

January 1, 1900. We set up the apparatus with the two right-angle prisms and obtained the patches. We found some difficulty due to stray light, which we nearly eliminated, so far as the outside of the apparatus was concerned, by inclosing it with screens. A cloth was placed over the arc and over the collimator and prisms, and a blackened canvas screen was hung up to divide the end of the room where the observations were made from the end containing the light But when matching pigments in a part of the spectrum in which they were nearly black, we were still able to perceive a small difference of colour in the two patches, which was due to internal reflections on the
 * Probably an error in reading.