51 |5 _a b_
b. With largest field. | 41.9 | 13.9 | 4.04 |5 _a a_
c. With field of 30 deg.. | 30 | 17.4 | 3.19 |5 _a c_
d. With field of 20 deg.. | 20 | 20.3 | 2.70 |5 _a d_
6. Glan's prism. | 7.9 | 50.3 | 0.831| 6
| | | |
II. THE NEW POLARISING PRISM. | | | |
1. With calc-spar: largest field. | 44 | 13.2 | 4.26 |5 _a a_
2. " field of 30 deg.. | 30 | 17.4 | 3.19 |5 _a c_
3. " field of 20 deg.. | 20 | 20.3 | 2.70 |5 _a d_
4. With nitrate of soda: | | | |
" largest field. | 54 | 16.7 | 3.53 |7 _a a_
5. " field of 30 deg.. | 30 | 24 | 2.25 |7 _a b_
6. " field of 20 deg.. | 20 | 27 | 1.96 |7 _a c_
---------------------------------------+------+---------+------+------
As an analyzing prism of about 6 mm. clear width, and 13.5 mm. long,
the new prism is stated by its inventor to be of the most essential
service, and it would certainly appear that the arrangement is rather
better adapted for small prisms than for those of considerable size.
Any means by which a beam of polarized light of large diameter--say 3
to 31/2 inches--could be obtained with all the convenience of a Nicol
would be a real advance, for spar of sufficient size and purity for
such a purpose has become so scarce and therefore so valuable that
large prisms are difficult to procure at all.
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