Five-feet Equatorial Instrument. 11 
scheme of its fabric was cast by the late Captain Huddart, 
many years a worthy Fellow of this Society. All the tinned 
iron work was made, under the direction and inspection of 
the same able engineer. Under the like superintendence 
also, was the brass work made, by J. and E. Troughton ; 
who having furnished it with graduation, reading micro- 
scopes, levels, &c. completed the instrument in 1797. The 
excellent object-glass for the telescope of 3J inches aperture 
was made by the late P. and J. Dollond. The power or- 
dinarily employed is 133; besides which, powers of 68, 116, 
240, 303, and 381, were occasionally used, being double eye- 
pieces ; and in some few cases a single lens with a power 
of 578 was employed for the purpose of minute scrutiny. 
The extent of the field with these powers (in their order 
beginning with the lowest, 68) was respectively 34/, 31', 20', 
* 9 '> 1 3'» 11# > and ....... . 
To preserve the tinned iron plate from oxidation, it has 
been well covered with white paint, and afterwards varnished ; 
thus it has not only a neat appearance, but can be cleaned at 
any time, without difficulty. 
The present situation of this instrument, in the immediate 
vicinity of one of the great thoroughfares of this immense 
metropolis, required the adoption of particular precautions 
against tremors. The northern pier is therefore sunk seven 
feet into the earth, where it is bedded on a Yorkshire flag 
four feet square, and two feet in thickness, into which the 
pier is firmly tenoned and fastened by stone wedges. From 
this flag rises a mass of brickwork to the level of the sur- 
face, surrounding the pier, and united with Parker's cement, 
having the area of its horizontal section equal to that of the 
