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CHAPTER II 



LOW-POWER WORK 



In this chapter, Section I., low-power photo-micrography and the apparatus used 

 are explained. 



Whilst Section II. is devoted to (i) development of the negative ; (ii) the making 

 of lantern slides ; and (iii) the printing of positives on paper. 



SECTION I.— LOW-POWER WORK 



It may surprise the reader to hear that, v/ith low-power work, the microscope is 

 entirely dispensed with, because the narrowness of the tube so curtails the field of 

 view that the resulting picture is practically of no service. To get over this difficulty 

 resort is made to the ordinary photographic camera, which for many purposes need 

 not be larger than quarter-plate size, having an extension of from twelve to thirteen 

 inches. We know, iti stating this, that many fellow-workers prefer one of larger, say 

 half-plate size, but after considerable experience, save perhaps for special pictures 

 required of much larger size than usual, the gain in use of a larger instrument we 

 have never found commensurate with the increase of cost both initially and to main- 

 tain, for it is self evident every half plate costs double that of a quarter plate. When 

 photographing bacteria, diatoms &c., where small fields are only necessary, we may 

 go still further and say the larger size is a decided hindrance, as the " carriers" for 

 the use of smaller plates are rarely fitted accurately enough, with respect to " register," 

 to admit of a really sharply focussed picture being taken. 



The arrangement of the apparatus in its entirety is shown in Fig. 9, which in a 

 measure explains itself Speaking in the first place quite generally, the camera is 

 supposed to be placed on a rigid support, and the lens is shown fixed in the front of 

 it. The object is placed at S, where it is supported in a manner to be further 

 described, whilst the illuminant is a limelight enclosed in a box provided with a 



I 



