276 Poivell and Lealand's 1-BOth. 



those pictures from abrasion on counters and tables. By atten- 

 tion to this, and by adopting the flat style of engraving — clear 

 in outline but not bold in relief — economy, elegance, and greater 

 durability would inevitably characterise the British coinage. 

 It should always be remembered that coins are intended to do 

 the work of * coins, and that they ought not to resemble 

 medallets, as too many of them at present do. 



POWELL AND LEALAND'S ^,th 



60 J 



The question of the use of high powers for the microscope is 

 rising in importance, and the argument is certainly in favour 

 of those who desire to obtain the greatest magnification con- 

 sistent with distinct vision, and convenience in use. The 

 relative merits of twelfths and twenty-fifths must be considered 

 upon the principles by which we estimate the comparative 

 advantages of eighths and twelfths, while the twenty- fifths will 

 have to be tested by comparison with the fiftieths, or any 

 higher power that can be got into working order. 



It is not desirable, when the finest definition is required, 

 that the power of any glass should be pushed indefinitely 

 beyond that which it will give with the first eye-piece usually 

 employed. With high powers, if more than double, or at the 

 outside triple, the enlargement produced by the employment 

 of the first eye-piece is required, it is usually much better to 

 resort to a deeper objective than to a deeper eye-piece. The chief 

 exceptions to this rule arise from the fact that, the deeper 

 objective must be brought considerably nearer the object, 

 while the focussing of a lower objective with a deeper eye-piece 

 is little changed. 



It is of no use to magnify an object more than is necessary 

 for its convenient display, and consequently it is only those 

 which are extremely minute that can be benefited by greater 

 enlargement than a good j^th will give. Suppose the perform- 

 ance of such a glass to be in perfection when not pushed 

 beyond 1500, a^th should be quite as perfect at 1000 more, 

 and a new ^th just made by Messrs. Powell and Lcaland is 

 exquisitely perfect when acting upon the Podura scale at 4000. 

 All the glasses we have named perform ivell at considerably 

 higher powers than we have named. It is hard to choose 

 between Ross's ,-Uh and Powell's J.th at 2000, though we think 

 at that range the latter has the advantage. It will be hard, 

 we apprehend, to choose between Powell's ^th and their .^th 

 at 3000 or 4000, though we expect the latter will have a slight 



