184 W. T. SUFFOLK ON DELINEATING MICROSCOPIC OBJECTS. 



application. In order that a microscopic object should yield a good 

 photograph, it is necessary that it should be very thin, so that the 

 greater part of it can be brought into focus at once, the reduction 

 of aperture practised successfully by landscape and other photo- 

 graphers not being available here on account of the great loss of 

 light caused by the use of small diaphragms. It is also requisite 

 in the present state of micro -photography that the object should be 

 such that all its details can be brought out by transmitted light, 

 and should be colourless, or at any rate of a colour not hindering 

 the transmission of the chemical rays of the spectrum. These con- 

 ditions, at present, limit very much the application of photography 

 to microscopic purposes ; and the necessity of employing special 

 apparatus, and mastering a somewhat delicate set of chemical pro- 

 cesses, will ever prevent its extensive employment. The photo- 

 graphs by Dr. Maddox, and those issued by the Medical Depart- 

 ment of the United States Army, show well the capabilities of the 

 art, — the markings of the Diatomacese being represented with a 

 minuteness and accuracy so great, that photographs on glass will 

 bear a considerable amount of enlargement, by means of the magic 

 lantern. There is exhibited this evening on one of the tables, a beau- 

 tiful series of micro-photographs, taken and presented to the club by 

 our President, which will enable those who are at present unac- 

 quainted with the results attained in this department of art to 

 judge of its merits for themselves. 



Drawing without auxiliary instruments is only available to experi- 

 enced artists, and is defective on account of its giving no key to the 

 dimensions of the object. It is chiefly of use for rough notes and 

 living objects in motion, where instruments would be of httle 

 service. 



The principal drawing instruments attached to the microscope 

 are Dr. Wollaston's camera lucida, Scemmering's steel mirror, and 

 the neutral tint reflector. These are mostly contrivances by which 

 the pencil and the paper and the image of the object are rendered 

 visible together, and apparently blended. This can be effected in 

 two ways. First, as in the camera lucida, Scemmering's steel mirror, 

 and Nachet's instruments, by viewing the image of the object with 

 one portion of the pupil of the eye, and the paper and pencil with 

 the other. Second, as in the neutral tint reflector, where the pencil 

 and the paper are viewed through the inclined mirror, which at the 

 same time reflects the image of the object. 



