105 



March 6, 1861. 



The President in the chair. 



Dr. Gould, in regard to the holes in the stone exhibited at the last 

 meeting, and said by Prof. Agassiz to have been excavated by Saxicava 

 rugosa, observed that the finding of this shell in the holes and fitting 

 them accurately, did not prove that tliey were the excavators. This 

 shell may enter a hole of any shape, and adapt itself exactly to it ; 

 and, from the habit of thus moulding its shell to the cavity in which it 

 lives, is often called Saxicava distorta. Crepidula has often been found 

 distorted so as to fit similar excavations, but that is no evidence that 

 it made the holes. Petricola in like manner frequently occurs in holes 

 made by pliolas and lithodomus. The fitting of the shell to the cavity 

 is rather an evidence of the power of adaptation in form, than of 

 ability to perforate. 



Mr. L. W. Bailey read the following communication on 

 Micro-Photography, or the photographic delineations of 

 microscopic objects, and presented, in the name of the author, 

 Mr. A. M. Eaton, of Providence, several ambrotypes of 

 diatoms. 



Micro-Photography, or the Photographic Delineation of 

 Microscopic Objects. 



Thinking that some details of the method by which J obtained 

 these ambrotypes, might not prove uninteresting to you, I propose 

 to lay before you a brief account of my experiments, and of the 

 method which I have found to be the most successful. 



As to the general arrangement of the microscope and of the 

 camera, I adopt the following plan, which is one quite generally used. 

 I remove the ordinary lenses of the camera, and substitute in their 

 place a sliding piece of wood, having a hole in the centre, so arranged, 

 that when hned with black velvet, the tube of the microscope (with 

 the eye-piece removed) when placed in a horizontal position shall 

 just sHde in it. 



At first, I tried to obtain negatives by lamp-light, from which nega- 

 tives I might obtain positives or conmion photographs in the usual 

 way. For this purpose, I placed the lamp directly in front of the 

 microscope, using no means to condense the light. This succeeded 

 quite well with low powers. In order to obtain a better illumination, 

 I then placed two large bull's eye condensers between the light and 

 the microscope, according to the method given in the Quarterly 

 Journal of Microscopical Science. I thus obtained a much better 

 illumination, but soon became satisfied that I should need sunlight in 

 order to succeed with the high powers. 



