Dr. Wollaston on the 
36 
figures 11 and is, the lines Im , no , mark the irregularities 
arising from defects in centering of the inner and outer con- 
vex glasses, as in fig. 13, the line pq, shows the error cor- 
respondent to a want of adjustment of the middle concave. 
By these guides alone I have now so repeatedly restored 
my object-glass to correct performance after having removed 
it from its cell, that I may venture, with considerable confi- 
dence, to recommend trial of the method to those who wish 
to perfect glasses of this construction. The degree of ac- 
curacy to be attained will depend upon the smallness and 
brightness of the light employed. 
For the purpose of merely seeing the series of images 
above described, the entire flame of a candle, not confined 
by an eye-tube, forms a set of very conspicuous images. To 
see that the images are not very irregular, an eye-hole of 
one-fourth or one-fifth of an inch may be used. When the 
intention is to commence adjustment by candle-light, a single 
eye-glass of one- tenth or one-fifteenth of an inch focus will 
be found to give a series of neat images very well suited to 
the purpose; but, for completing a very nice adjustment, I 
have found it necessary to employ the light of the sun, and 
a still smaller lens of one-twentieth or one-thirtieth of an inch 
focus. With this view, there is no occasion to point the tele- 
scope to the sun, for if his light falls even very obliquely on 
a small eye-glass, the exterior images Ad, and A f, are mere 
luminous points, so that any error in their relative position 
is immediately detected. 
With this test, as guide for final adjustment, and without 
farther revision, the telescope on which this method has been 
tried, is capable of either separating very small and nearly 
