Light visible and invisible; a series of lectures delivered at the Royal institution of Great Britain, at Christmas, 1896, with additional lectures

by Silvanus Phillips Thompson

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1897 ...I now take two prepared pieces of mica, which will be exhibited to you first separately and then together. One of them shows the blue of the second order, a tint which by reference to the table is the same as that produced by an air film 13 millionths of an inch thick. The other shows a yellow of the second order, corresponding to an air film 18 millionths of an inch thick. Now guess what will happen if they are both put in together. Will blue and yellow make green? Not by any means. If superposed (with their axes both at 45 to the right) they will have the same effect as a piece of mica would have if its thickness was equal to that of the two added or it will act as a film of air in the Newton's rings 31 millionths of an inch thick, giving a tint which, by the table, you see to be a rose red. My assistant slides one crystal over the other (Fig. 97) and you observe in this case the unexpected, though predicted, result that blue and yellow added in this way make pink. Let one of the crystals "" now be turned about so as to put its axis 45 to the left, so that it will act negatively, giving the same result as if we had subtracted one thickness from the other. What tint ought it to give? Sub trading 13 millionths (blue) from 18 millionths (yellow), we obtain the answer that it ought to give the same tint as an air film 5 millionths of an inch thick, which tint is a grayish white. Look for yourselves and see how on the screen where the blue (reversed) crystal overlaps the yellow crystal, the resultant tint is a grayish white. The next object is a wedge combination made of twenty-four very thin pieces of mica set to overlap one another, so as to form a wedge in steps. It, like the smooth wedge of selenite, gives the Newton tints of the first ...

66 pages, Paperback

First published September 27, 2015

About the author

Silvanus Phillips Thompson FRS was a professor of physics at the City and Guilds Technical College in Finsbury, England. He was known for his work as an electrical engineer and as an author.

Thompson is one of the individuals represented on the Engineers Walk in Bristol, England.

Thompson was elected a Fellow of the Royal Society in 1891 and was elected a member of the Royal Swedish Academy of Sciences in 1894.