THE PHOTO-MICKOGEAPHIC CAMEKA 123 



a large milled head at its end near the focussing-screen. At the 

 other end is a grooved pulley, and between this and the 

 fine-adjustment of the microscope a connection is made, 

 usually consisting of a light cord which passes from one 

 to the other. This is preferably a silk thread well rubbed 

 with bees'-Wax so that it is not liable to slip on either pulley ; 

 in any case it should be taken from one to the other so 

 that there is no strain ; in fact, it will be found that with 

 waxed silk a very loose connection will quite efficiently turn 

 the fine-adjustment screw, and that it will respond immediately 

 to changes of direction. Some inexpensive additions to this 

 type of apparatus will increase its efficiency very greatly. It 

 is convenient to be able to make an observation in the micro- 

 scope, or to alter any of the adjustments while observing 

 the image directly through the instrument. This may be 

 effected in two ways : either by carrying the microscope and 

 the illuminant on a separate board or support, as shown, 

 and so arranging it that it can be swung out on a central 

 pivot as an axis ; or, as in the types of apparatus devised 

 by Messrs. Zeiss, the microscope itself may be on a sliding 

 base so that it can be moved laterally in or out of the axis 

 of the whole apparatus. The former method is preferable, 

 as there is then no alteration in the relative position of 

 the optical system and the illuminant: when the turntable 

 is swung round it allows an observer easily and conveniently 

 to adjust the light, or any of the sub-stage illuminating 

 apparatus, without having to watch the effect of any such 

 alteration on the focussing-screen of the camera. 



The apparatus (Fig. 43) embodies both the arrangement 

 for focussing from a distance, and also a simple form of 

 turntable carrying the microscope, and, as it is reasonably 

 stiffly built, it would answer for moderately high-power work. 

 If, however, an apparatus is required that will enable any class 

 of work to be attempted, then still further elaboration is 

 advisable. 



Figs. 44 a and & illustrate an apparatus made by Messrs. 

 Koss of New Bond Street, London, which embodies all the 

 requisite adjustments. It is designed for use both for 

 transmitted and incident light, so that it is available for 

 metallurgical or similar work in addition to the photographing 



