806 Dr. maskelyne’s Account of 
caufe fmall angles are proportional to their fines, and the 
fine of NR£ is equal to the fine of its fupplement nrc) 
is to ncr as nc or ce is to nr or rc. In like manner, the 
ray wgr, which belongs to the axis wco, and is refradted 
by the prifm rs to 210 or e, undergoes the refraction or e, 
which is to oce as oc or ce is to ro or rc; therefore, by 
compofition, orn the fum of the reffadtions ORq nrc, is. 
to ocn the fum of the angles oc e, ncc, or the Sun’s ap- 
parent diameter, as ce to rc; that is, as the focal diftance 
of the objedt-glafs to the diftance of the prifms from the 
focus of the objedt-glafs. 
Or let the prifms pr, rs, be placed with their refract- 
ing angles p, s, turned from one another as in fig 4.: 
the refraction of the prifm pr will transfer the image of 
the Sun from on to we, and the refruCtion of the prifm 
rs will transfer the image on to 2W2e, the two images 
2W2e, we, touching one another externally at the point 
2 £W. Let ecn, wco, be the axes of the pencils of rays 
proceeding from the two extreme limbs of the Sun, and 
N, o, the points where the images of the Sun’s Eaftern 
and Weftern limbs would be formed by the objedt-glafs, 
were it not for the refraction of the prifms ; the ray efr, 
which belongs to the axis ecn, and is refraCled by the 
prifm rs to 2c, undergoes the refraction nr 2c; and the 
ray wgr, which belongs to the axis wco, and is refradted 
bv 
J 
