34 PKOGKESS OF MICK08C0PICAL SCIENCE. 



Diatoms thrown up hy the Sea. — Mr. E. Bicknell, of the Museum of 

 Comparative Zoology at Cambridge, Mass., exhibited some diatoms 

 recently thrown up by the sea at Marblehead, Mass. The deposit first 

 found belonged to brackish water, as indicated by the nature of the 

 diatoms and the presence of fruit of the Characece. The second deposit 

 occurred about a mile fi-om the first, and was purely of fresh-water 

 origin ; consisting of peat with fresh-water diatoms, — Pinmdaria, 

 Stauroneis, Navicida rhomboides, N. serians, &c. These deposits were 

 thrown up by a severe storm on the 31st of March last, and are 

 believed to be the first fresh-water or brackish deposits known to exist 

 under the present ocean. They seem to be conclusive proof of the 

 recent encroachments of the ocean upon the shore-line in that vicinity. 



The Test-plate of Nohert, who has now " gone to the war," and Dr. 

 Woodward's photographs of the same, were exhibited by Dr. Ward, 

 chiefly in the interest of that part of the audience who were not profes- 

 sional microscopists, and might be unfamiliar with these wonderful 

 works of human art. Until a year or two ago the finest lines had 

 never been seen, even by the maker of them ; now they have been seen 

 by many persons, and have been photographed. He was now satisfied, 

 for the first time, after hearing Mr. Bicknell's description, that the 

 Boston microscopists had seen the genuine lines with powers of only 

 five or six hundred diameters. In regard to the use of photography 

 as a test of structure under high powers and difficult circumstances, 

 we may learn a lesson from the broad bands of light and shade in the 

 photograph of the coarser lines, which manifestly have no resemblance 

 to the appearance of scratches on glass as seen under suitable powers. 

 Dr. Ward had also been investigating the ejffect of seeing two planes 

 of the object at the same time with the Wenham's binocular. The 

 eye-pieces being practically not equidistant from the objective, the 

 corresponding conjugate foci below do not coincide. Some microscop- 

 ists have attributed much of the stereoscopic effect to this fact, which, 

 however, does not seem to contribute perceptibly (except in the lowest 

 powers, where the angular stereoscopic effect is necessarily very small, 

 and where this difference of planes is most considerable) either to the 

 stereoscopic effect or to the increased distinctness of definition above 

 and below the plane of most perfect vision. 



Microscopes Exhibited. — An abundance of instruments were fur- 

 nished by members to illustrate their discussions, or for the general 

 work of the subsection. The first-class stands were mostly of the make 

 of Powell and Lealand, and Beck, and Crouch, of London, of Nachet 

 of Paris, and of Zentmeyer in America. The " Jackson " model of 

 stand, with a curved arm, seems to be growing in favour in America ; 

 and it is to be hoped that those makers who have heretofore made 

 only one style of stand will soon offer both ; so that buyers can choose 

 their style of stand irrespective of their choice of makers. In objec- 

 tives and accessories, ToUes, Wales, Zentmeyer, Grunow, Spencer, 

 Miller, and some other American makers were represented ; also Eoss, 

 Beck, Powell and Lealand, Crouch, Collins, Murray and Heath, Swift 

 and Browning, of London ; Nachet and Hartnack, of Paris ; and 

 Gundlach, of Berlin. Very low-power objectives, 3 and 4 inch, were 



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