*^jounlL;MS-ti^^^^^^ Construction of Object-glasses. 295 
naturally no magnetizable iron, save such as has comparatively 
recently fallen from outward space. The savage tips his weapon 
with this meteoric iron : the more advanced man, dealing with the 
"ore," drives out the oxygen, the affinity of which for the metal 
has rendered all iron coeval with the earth defunct as regards the 
power of being magnetized. Other affinities affect " sarcode " in a 
much shorter time, and sooner render the jelly-speck defunct. But 
the difference is one of degree, — is not absolute as respects the time 
in which revitalizing or remagnetizing be possible. 
Knowledge is limited and suggestive of opinion and belief as 
to the vast unknown ; for guidance toward which opinion analogy 
alone, for a time, can be offered. To treat analogy as if identity 
had been predicated (e.g. "if the magnet moved itself" — "if it 
divided and multiplied if every part of it were capable of 
moving" — "if it were able to select," &c. &c., p. 179), is more 
Hkely to mislead than to guide, I presume P. B. to hold an 
opinion or belief as to the vitalization of the primary granule or 
jelly-speck opposed to " nomogeny," or my conception of the powers 
assigned to the waters that, of old, abundantly brought forth the 
living and moving entities. The analogies supporting the alter- 
native behef — thaumatogeny — would be more instructive than 
banter: but the party against which that weapon is used may 
take encouragement from the ' History of Controversy,' that it 
is groping in the right direction. 
Y. — On the Construction of Ohject-glasses for the Microscope. 
By F. H. Wenham. 
{Continued from page 228, No. IV.) 
For the brass setting of object-glasses, it is necessary that the 
worker should possess a good foot-lathe; if provided with a self- 
acting arrangement for chasing up the short screwed parts of the 
cells, this will ensure greater accuracy of workmanship. The 
setting or metal work of an object-glass must alv/ays be made 
before the lenses are commenced ; three steel gauges are to be first 
formed, of a width exactly corresponding to the diameter of the 
intended lenses ; this gauge I make out of a piece of sheet steel, 
with three arms of the three diameters required. A chuck should 
be fitted to the lathe, and cut out to the standard thread now 
generally adopted for object-glasses ; into this the brass setting is 
fitted, and each cell screwed on, and turned out in succession to the 
proper size. I leave no shoulders at the back of the cells, but bore 
them clear through. 
