202 Mr. Harvey on Chronometers. 
In like manner, by referring to the case in which a’ is greater than 
a, the numerical value of the function will assume a positive charac- 
ter, and the chronometer will gain. 
Thus, with changes in the amplitude of the arc of vibration, from 
less to greater, or from greater to less, resulting from the applica- 
tion of a disturbing force in different directions, will results entirely 
opposite in their character be produced in different chronometers, 
in consequence of Varieties of Imperfect Isochronism. 
Plymouth, May 20, 1824. 
Art. Ill. On Indistinctness of Vision caused by the presence 
of False Light in Optical. Instruments, and on tts Reme- 
dies. By C. R. Goring, M. D. 
[Continued from p. 28] 
Microscorts.—These instruments though but toys compared 
with telescopes, nevertheless deserve to be rendered as perfect as 
possible, for they yield not to them in the quantity and variety of 
rational amusement which they are capable of introducing us to 
(though not of the sublime description of the wonders of the 
heavens). Compound microscopes though not so much to be 
depended upon for the purposes of discovery and philosophical 
investigation as single lenses, are still best adapted for recreation, 
but all those which I have ever seen constructed on the common 
principle, are so full of fog as to be quite disagreeable for exami-- 
ing opaque objects, which render this defect more striking than 
transparent ones. This false light results from the custom of 
making the object-glass of a very small aperture, instead of giving 
it a larger one, and placing a stop in its proper place (the focus 
of the lens employed). It is totally impossible to get rid of the 
fog in any other way. No doubt the larger the aperture of the 
lens of the common object-glass, the more indistinctness is sen- 
sible ; and the more it is reduced, the less;—but no practicable con- 
traction of the aperture will effect the desired purpose completely, 
