q 48 Mr. Wollaston’s Defcription of a 
year (lip by, without making it known ; knee, I think, from 
what I have done with it, I may be confident of its utility*. 
The properties and advantages of fuch a fyfietn of wires 
fcarcely need to be pointed out to aftronomers. The whole ex- 
tent of the field is employed as it is in the rhombus (the want 
of which was fa i d to be Dr. Bradley’s objedlion to M. Cas- 
sini’s wires) ; but being formed of right angles or half- right 
angles, to which workmen are moft accuftomed, they will 
always be apt to execute their part better; and the obliques, 
from the differences being juft double to what they are in the 
rhombus, give the) comparative declinations with twice the 
certainty. To this the number of correfponding obfervations 
in the paffage of every ftar add confiderably ; fince you may 
calculate its diftance from the center C, from the angle D or E ? 
or from one of the intermediate angles K, as you lhall fee occa- 
fion. The fame indeed you may do in the rhombus from D or 
from E; or, if the rhombus be formed of wires, from the 
angle at L, fig. 2. ; but only with half the precifion. The 
refult of a tingle paffage of any one ftar (excepting towards the 
extremities of the field) gives the extent of the field equally in 
each, provided the declination of the ftar be known, by de- 
ducing its diftance from thofe leveral angles ; and fuch deduc- 
tions ferve as a ftill farther check upon every obfervation ; be- 
* What is here offered is by no means to be underftood as recommending any 
fvftem of wires in preference to aflual meafurement with a micrometer, but to 
render the xife of them as convenient as may be to fuch gentlemen as are not 
provided with better inftruments. The equatorial micrometer with a large field 
(fuch as I have feen at Mr. Aubert’s, of Mr. Smeaton’s conftruftion) I take to 
be the belt xnftrument for taking differences of right afcenfion and declination 
out of the meridian ; and far fuperior to any fyllena of fixed wires, or indeed to 
any equatorial fe&or whatever. 
caufe, 
