ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
399 
little enhanced i^rice pressed discs of the same glass having the approxi- 
mate form of the desired lens can be obtained. 
No. 
Fabric 
No. 
Description. 
1 Refractive 
Index D. 
Medium 
Dispersion, 
C-F. 
Specific 
Gravity. 
15 
0-599 
Boron silicate crown 
1-5069 
0-00813 
2-48 
46 
0-337 
Silicate crown 
1-5111 
0 • 00817 
2-60 
17 
0-371 
1-5109 
0-00811 
2-48 
48 
0-516 
Flint crown . . . . . . . . 
1-5170 
0-00859 
2-59 
49 
0-567 
Silicate crown 
! 1-5134 
0-00859 
2-51 
50 
0-610 
Crown of low dispersion 
1-5063 
0-00858 
2-51 
51 
0-598 
Silicate crown 
1-5152 
0-00879 
2-59 
52 
0-512 
M 5? 
1-5195 
0- 00886 
2-61 
53 
0-463 
Baryta light flint 
1-5616 
001020 
3-11 
51 
0-608 
Crown of high dispersion .. 
1-5149 
0-00942 
2-60 
55 
0-602 
Baryta light flint 
1-5676 
0- 01072 
3-12 
56 
0-381 
Crown of high dispersion .. 
1-5262 
0*01026 
2-70 
57 
0-583 
Baryta light flint 
1-5688 
0-01110 
3-16 
58 
0-513 

1-5637 
0-01115 
3-11 
59 
0-527 
5) 5? 
1-5718 
0-01133 
3-19 
60 
0-575 
n 99 
1-5682 
0-01151 
3-15 
61 
0-522 
99 9 9 
1-5551 
0-01153 
3-03 
62 
0-578 
99 99 ^ 
1-5825 
0-01255 
3-29 
63 
0-376 
Ordinary light flint 
1-5660 
0-01319 
3-12 
61 
0-310 
99 99 
1-5774 
0-01396 
3-21 
65 
0-569 
9 9 99 • • • • • • 
1-5738 
0-01383 
3-22 
66 
0-318 
99 99 
1-6031 
0-01575 
3-48 
67 
0-266 
M »» 
1-6287 
0-01775 
3-72 
68 
0-335 
Dense silicate flint 
1 - 6372 
0-01831 
3-77 
Lehmann’s Molecular Physics."^ — The following review of Dr. 
Lehmann’s treatise is taken from a recent number of ‘ Nature, where it 
appeared under the title of “ The Application of the Microscope to 
Physical and Chemical Investigations ” : — 
Very soon after the first invention of the Microscope, attempts were 
made to apply the new instrument to solve some of the remarkable problems 
of crystallogenesis. The early volumes of the Royal Society Transactions 
contain in the papers of Boyle, Hooke, and Leeuwenhoek, published 
between the years 1663 and 1709, many records of attempts of this kind; 
and the works of Henry Baker, which appeared between 1744 and 1764, 
are also largely concerned with the study of the process of crystallization 
under the Microscope. 
In Germany, Ledermuller in 1764, and Gerhardt in 1780, showed 
the value of the Microscope in studying the internal structure of crystals ; 
while in France a long succession of enthusiastic investigators, Dauben- 
ton, Dolomieu, Fleurian de Bellevue, Cordier, and others, were busily 
engaged in laying the foundations of the science of microscopical 
petrography. 
Early in the present century, we find the English investigators once 
‘ Molekularpliysik, mit besonderer Beriicksichtigung mikroskopischer Unter- 
suehungen und Anleitung zu Solchen, sowie einem Anhang ilber mikrochemische 
Analyse.’ Von Dr. O. ‘Lehmann, Professor der Electrotechnik am kgl. Polytecli- 
nikum zu Dresden. Leipzig (W. Engelmann), 1888-9, 2 vols., pp. 852 and 697 
(621 figs, and 10 pis.). t Nature, xlii. (1890) pp. 1-2. 
