338 
ON THE EQUATORIAL TELESCOPE, 
A'^arious 
improvements 
proposed to 
render this 
instillment 
more exten- 
^ciy useful. 
excellent achromatic object glass, was furnished with but a very 
small degree of magnifying power. My chief design In staling 
these circumstances, is, with all due deference to their superior 
skill, to suggest to Messrs. Jones, or any other gentlemen 
who manufacture such instruments, that, by a slight addition, 
and variation, they might be made much more interesting to 
students of astronomy, and capable of more general and ex- 
tewsive application ; and their moderate price might induce 
many who have a taste for astronomical science to procure such 
an instrument, who, otherwise, might never have thought of 
purchasing a similar apparatus on a larger scale. 
The improvement to which I allude, is the substitution of a 
larger telescope, in place of the small one which generally 
accompanies the instrument, furnished with four eye pieces of 
different magnifying powers. The achromatic object glass 
(which should be a very good one) might be from 17to22 
inches focal distance, and about 2 inches, or nearly so, in 
diameter. One of the eye-pieces might be a diagonal one, 
A 
carrying a power of about 20 times; another an erect eye- 
piece, having a power of 30 ; and two astronomical eye-pieces, 
with powers of 60 and 80 times. It would not be necessary 
that cross-wires should be connected with any more than one of 
the eyc-pieccs ; as the higher powers would be chiefly used for 
viewing celestial phenomena by day or by night ; in which- case 
the want of the wires is rather an advantage. It will be 
obvious, too, that in a telescope of such dimensions, furnished 
with such powers, instead of the sliding tube at the object-end, 
which produces a tremor in the instrument when adjusting the 
glasses to distinct vision, the adjustments should be made near 
the eye-end, by teeth and pinion, as in the larger sort of 
achromatic telescopes. It will also add to the general utility of 
the instrument, if one of the eye-pieces be furnished with one 
of Cavallo’s pearl micrometers, which will add but a few 
shillings to the expence.— -The chief objection that can be made 
to this suggestion will probably be, that the telescope would be 
too large and unwieldy in proportion to the dimensions of the 
equatorial 
