THE 
PHILOSOPHICAL MAGAZINE 
AND JOURNAL. 
I. Description of a new Transit Instrument. By Sir H.C, 
ENGLEFIELD, Bart. F.R.S. F.S.A. Sc. ic. Ce. 
Taz transit instrument, of which I propose to give a descrip- 
tion, was thought of in consequence of a request from Mr. Thomas 
Jones, astronomical, &c. &c. instrument maker, in Oxendon- 
street, who, having been often applied to by watch-makers, and 
others not much conversant with astronomy, to make for them 
a cheup, simple, and easily placed instrument, for the purpose 
of obtaining time with accuracy, requested me to assist him 
with my ideas on the subject. 
An old transit instrument formerly belonging to Mr. Aubert, 
and at his sale purchased by Mr. Walker, gave me the first hint 
for the instrument now to be described, It had, like this, its. 
telescope in the axis; but the reflecting mirror was between the 
object- and eye-glasses, which rendered it cumbersome, and liable 
to many inconyeniencies, which are, I think, avoided in the mode 
of construction now adopted. 
It may be here observed, that Hevelius, in his Selenographia, 
describes a telescope in which a mirror is interposed between the 
object-glass and eye-piece, thereby enabling an observer, without 
danger, to look out of a besieged place, the telescope being 
placed vertically under shelter of the rampart. It seems singular 
that he should not have perceived how much more commodious 
and simple his instrument would have been, had the mirror been 
placed beyond the object-glass, and made so as to turn all round, 
as it has been of late years made to do in some of the large 
camera obscuras. 1 
To return to the present subject. It is well known that the 
transit instrument, in its usual form, is liable to great injuries 
from blows, or other violence affecting the perpendicularity of 
the telescope to the axis; that it necessarily takes ap much 
room in package; that, unless of a very small size, it is not easily 
Vol, 43, No. 189, Jan, 1814, A fixed 
