24 PRACTICAL PHOTO-MICROGKAPHY. 



which pivot should be so arranged with the working part of 

 the swing that the microscope shall be steady at whatever 

 angle from vertical to horizontal it is placed. At true 

 horizontally the tube should be stopped by a " stop " for the 

 purpose. The body-tube of a stand for our work can hardly 

 be too wide in diameter so long as we do not reach the point 

 of inconvenience in adapting eye-pieces, etc., to the tube. 



The finest stands made, so far as the writer knows, are those 

 of Powell & Lealand, of London ; they are perfect in rigidity, 

 in mechanism, in workmanship and finish, and, though expen- 

 sive, their owners say they are cheap in the long run. 



A very good stand is the " Wales" pattern of Messrs. Swift 

 and Son, London. (Fig. 2.) The advantage of this form of 

 swing is that the centre of gravity is in the same position, and 

 that a good one, to whatever angle the tube is swung. The 

 writer used this stand for high power work with complete 

 satisfaction, and that he gave it up was due not to the stand 

 itself, but to certain exigencies which arose and could not be met 

 with the then arrangement whereof this stand formed a part. 

 Consequently this stand is highly recommended to those who 

 desire a good stand for our purpose at a very moderate price 

 considering the work, and the efficiency. For simple examina- 

 tion of objects, this stand fitted with a Differential Screw Fine 

 Adjustment, is a most satisfactory instrument for any kind of 

 work. 



Beck's Stands, which are easily procurable in America, are 

 probably in no way inferior to others, but we cannot speak 

 from personal experience. 



A most excellent stand is the one now exclusively used by 

 the writer for photo-micrography. In general the stand is the 

 so-called " Nelson " pattern, and the one in question was made 

 by Mr. 0. Baker, of London, specially for the writer. This 

 stand was made extra heavy and strong in all parts, with a 

 differential- screw fine adjustment most accurately fashioned, 

 and there is a similar fine adjustment to the sub-stage. A 

 very important feature not often attended to in stands of 

 modest pretensions, is the rack work draw-tube for the cor- 

 rection of objectives not furnished with " correction collars," 



