JOHN BOCKETT ON A NEW LOW-rOJVER OBJECT GLASS. 17 



When, ho-wever, this statement is considered carefully, it will be 

 seen that it requires very little refutation. No hand-glass of 

 simple construction can give that definition and freedom from 

 distortion which a lens constructed upon the usual principle upon 

 which microscope objectives are made affords. With the formei", 

 both hands are occupied; to say nothing of the unsteadiness, 

 it is also impossible that the illumination of the object can be per- 

 fect, added to which the nou-achromaticity and spherical aberration 

 exercises anything but a good effect upon the eyes ; neither can 

 the polariscope be used, nor can we obtain the effect of dark ground 

 illumination. To sum all up, the observer simply makes the best 

 use of a makeshift instrument, and is compelled, to a certain degree, 

 to guess at details he never could have seen. On the other hand, 

 with the new glass we have the sharpest definition ; it is, of course, 

 attached to the ordinary instrument, and has, therefore a solid stand, 

 free from all tremor. The illumination, whether for opaque or 

 transparent objects, is completely under control ; it is achromatic, 

 and pecuharly adapted for the binocular ; and its applicability to 

 Botany, Mineralogy, and Natural History, &c., &c., cannot be 

 questioned. It certainly requires a very long bar, on account of its 

 focus ; but the difficulty is easily overcome, by adapting to the top 

 of the bar a lengthening piece, which is not unsightly, soon fitted, 

 and inexpensive. Upon bringing the glass to bear upon all the 

 tests alluded to by Dr. Carpenter (page 192 of his last edition of 

 the Eevelations of the Microscope) specially pointed out for low 

 power objectives, one and all are beautifully shown. For Aquaria, 

 owing to its depth of focus, it is possible to see throiigh a con- 

 siderable thickness of water, and as small tanks, if not of consider- 

 able size, can now be made available, doubtless the study both of 

 animalcules and minute vegetation will be much enhanced. I will 

 only add that the recent small travelling microscopes take the power 

 without any alteration. The amplification, with the vai'ious eye- 

 pieces, will be found as under : — 



With the A, 9 ; B, 15 ; C, 26; D, 42; E, 64; F, 86. 

 Some of the new glasses are on the tables, so as to afford the 

 members of our Club every opportunity of judging for them- 

 selves. 



