Powell and Lealand's 1-hOth. 277 



advantage at the higher figure. The ^th gives a good view of 

 an object up to 9000, — so say some of its niost experienced 

 possessors, and from what we saw of the |jth, we have no doubt 

 its capacities will prove equally extensive. Pushed to their 

 extremes, fine glasses may often furnish some unexpected 

 information, but their choicest and most reliable work will be 

 far below their utmost range. The physiological inquiries 

 conducted by Dr. Beale show that very great enlargement is 

 necessary in order to trace the minuter nerve-threads, and see 

 how they stand in relation to nerve- cells. The vibrions 

 are not likely to yield the secrets of their organization to any 

 ordinary powers, and some of their family are scarcely visible 

 when magnified 2000 times. Great interest is felt to discover 

 how structures begin; whether by liquid matter solidifying, or 

 whether some small solid molecules are present at the com- 

 mencement, and by their coalescence form tissues and organs. 

 A glance at the protoplasmic fluid circulating in the Anacharis, 

 or the Vcvlisneria, when viewed with a magnification of 2000 

 linear, will serve to reveal a multitude of minute bodies, whose 

 proceedings and origin we should like to be acquainted with, 

 and if we are to gain such information, extreme magnification, 

 with exquisite definition is our only chance. 



Messrs. Powell and Lealand have shown that a -^th can be 

 made to define minute objects as perfectly as an inch glass 

 deals with large ones, and the new objective works through 

 glass about '003 thick. This is very good, and we do not 

 doubt it will be found useful in able hands, although nothing 

 short of a series of careful experiments can show when and 

 where it is superior to the ^th. 



We must, in discussing these high powers, again revert to 

 the importance of increasing their penetration and focal dis- 

 tance to the utmost limits which optical skill can devise. The 

 extent to which this can be carried will very much depend on 

 the material the glass maker can provide. If he can go on 

 increasing the density and refractive power of glass, a new 

 era in optical science will arise. Meanwhile it is a matter of 

 optical formula, and the distance at which Smith and Beck's 

 c^th will focus, shows what can already be done. 



