Monthly Microscopical"! 
Journal, Feb. 1,1869. J 
Ohjed-glasses, 
111 
Y. — On the Construction of Ohject-glasses for the Microscope. 
By F. H. Wenham. 
In introducing this subject, I must state that my practice has been 
merely one of experimental inquiry relating only to the construction 
of the highest powers, and as the results have been admitted by 
numerous comparisons to be satisfactory, I venture to assume that 
the methods employed by a self-taught amateur may form some 
useful addition to our stock of knowledge, and be of service to 
others who are inchned to pursue this light and elegant department 
of mechanical manipulation. 
The directions for working glass surfaces to a correct figure, 
may appear to some too practical and characteristic of the work- 
shop ; but it is only by a strict attention and study of such details 
that perfection can be ensured, and without their aid the deductions 
of the mathematician must fail in their proof. Though the early 
training of a mechanical profession has familiarized me with such 
pursuits, yet I must confess that I am ignorant of the methods 
adopted by our best makers for working their minute object-glasses ; 
and therefore if some particulars may have the merit of originality, 
others are perhaps not in accordance with the most improved 
practice. 
I have received numerous letters at various times from different 
microscopists requiring information on these subjects ; and as the 
whole science of microscopy is quite a practical one, I have good 
reason for knowing that any information relating to this point will 
be welcome to many, and be some atonement to those who have 
applied for instructions, and to whom I now make my apology, on 
the plea that the very limited time that has been at my disposal for 
the last ten years would not permit me to recall particulars that 
I had ceased to practise, or to enter 
into long written explanations upon 
the conations of failure or success 
submitted to my notice. I now pur- 
pose from time to time to publish the 
results of such experience as I have 
acquired. 
The first attempt to construct an 
object-glass {\ in.) is recorded in the 
year 1850, on the then well-known 
form shown by the cut. The back 
lenses had an excess of negative aber- 
ration, or were over-corrected, to enable the adjustment for covering- 
glass to be performed by the separation of the front lens, which was 
