274 THE MICROSCOPE. 
formance of these objectives, especially for those for homogene 
immersion.” 
When used with short tubes the performance of all objectives 
is affected in ways that are objectionable, but in ways that the 
beginner would not notice for himself. When the tube varies 
but little from the standard, the bad effects are not so great nor 
so noticeable; it is only on the very short bodies that they 
become prominent. When the non-adjustable objectives are 
used on standard bodies and the draw-tube is much extended, 
the results are equally bad, and the beginner will often read of 
objectives “ not bearing” such treatment, and “ breaking down,” 
which means that the image becomes so altered for the worse 
that it is worthless. This difficulty can never be feared in stands 
supplied with a short body which must have the draw-tube 
extended to obtain the standard length, but only on ten inch 
bodies when lengthened by the draw-tube. Neither will any of 
the troubles referred to be incurred to nearly so great an extent 
with low power objectives, such as the five, three, two or one 
inch, which, even the very best made by any optician, are 
always non-adjustable. It is with the higher powers, the one- 
fifth, one-fourth and higher, that the results become objection- 
able. But, as already said, the beginner would not notice the 
objectionable features introduced by changing the length of the 
tube; he would only be likely to see the alteration in the mag- 
nifying power. 
For these reasons the beginner would do well to reject an 
instrument whose body is much shorter than the standard length 
of ten inches, unless he wants his microscope as a toy to be 
played with for a short time, and to be then packed away on a 
shelf and forgotten. If he wants it for the examination of 
the exquisite beauties in Nature, if he intends to do any original 
investigation with it, then he most surely should avoid a stand 
with a short tube. And if he expects ever to use good objectives, 
_ if he expects his microscopical education ever to be improved, 
if he does not expect always to remain studying the microscop- 
ical alphabet, then I would, as a disinterested adviser, earnestly 
urge him to avoid a stand with a very short body-tube. These 
chapters are written for those beginners who have some serious 
purpose in view when they buy a microscope; something more 
serious, indeed, than mere amusement, although there is nothing 
