94 



nearly aa good as when it was fresh gathered, and the spectrum 

 reaction quite perfect. 



Mr. Carruthers read a paper on the " Plants of the Coal- 

 measures." 



Mr. Slack wished to call the attention of Fellows conversant 

 with crystallography to the curious instance mentioned by Mr. 

 Carruthers, in which, after the charring of the vegetable struc- 

 ture, although the particles of carbon preserved the exact form of 

 the vegetable cells, they had opposed no obstacle to the crystalli- 

 zation of the carbonate of lime, which had gone on through their 

 interstices as though no obstacles had intervened. 



Mr. C. Brooke stated that structure is much interfered with 

 by foreign matter — the sandstone of Fontainebleau, for instance, 

 assumes the form of rhombohedral crystals of calcite. The stone 

 does not contain more than 5 to 7 per cent, of carbonate of lime; 

 but the 95 per cent, of silex seems to be dragged into form by 

 the 5 per cent, of carbonate of lime which controlled the character 

 of the crystallization. 



A paper was read from Brevet Lieut. -Colonel Woodward, 

 Assistant Surgeon of the United States army, on " Immersion 

 Objectives and Nobert's Test-plate." 



The ' Quarterly Journal of Microscopical Science ' for October, 

 18G8, contains (p. 225) a short article in which I record the 

 results of certain experiments made by me with the new nineteen- 

 band test-plate of Nobert. In that paper I stated that I had 

 obtained the best results with the J^th objective of Messrs. 

 Powell and Lealand, of London. The ^'^th of these makers, which 

 in my hands had excelled their J^^th on Podura and other test- 

 objects, proved inferior on this plate, apparently because the 

 cover of the object was too thick to allow the lens to do its best. 

 With the oVth I satisfactorily resolved the true lines of the 

 fifteenth band of the plate ; and subsequently my friend and 

 assistant, Brevet-Major E. Curtis, Assistant-Surgeon, U.S.A., 

 prepared a series of photographs of the several bands, showing 

 the true lines in each, from the first to the fifteenth inclusive. 

 I was, however, unable to make out the true lines in the last four 

 bands with any lens then in my possession. I conceived the idea, 

 nevertheless, that if I could procure a test-plate ruled on a 

 thinner cover, so as to give the J^th full play, I might go farther. 

 I therefore wrote to Nobert, who, after long delay, furnished me 

 with a new test-plate, which reached me during March of the 

 present year. This test-plate cannot be too highly praised for its 

 delicacy and beauty. The lines are ruled on the under-surface of 

 a square of thin glass the oy^-th of an inch thick, whicii is ce- 

 mented to a glass circle the -fio^^^ ^^ ^^ ^"^'^ thick. This circle 

 is mounted over a round aperture in a strip of burnished brass 

 3 inches by 1, on which is inscribed the usual memoranda placed 

 by Nobert on his nineteen-band plates. 



The results of using this test-plaie are as follows : 



A careful count of the lines in each hand, with Messrs. Powell 



