2i 6 Dr. Herschei/s Observations 
micrometers, joined to what I have mentioned above, of 
using the disk-micrometer without lamps when day-light is 
sufficiently strong ; or even with an illumination in front, 
where the object is bright enough to allow of it, such as the 
moon, &c. 
I remember drawing the picture of a cottage by it, in the 
year 1776, which was at three or four miles distance; and 
going afterwards to compare the parts of it with the building, 
found them very justly delineated. 
I have also many times had the honour of shewing my 
friends the accuracy of the method of applying one eye to 
the telescope, and the other to the projected picture of the 
object in view ; by desiring them to make two points, with a 
pin, upon a card fixed up at a convenient place, where it 
might be viewed in my telescope ; and this being done, I 
took the distance of these points from the picture I saw pro- 
jected, in a pair of proportional compasses, one side of which 
was to the other as the distance of the object, divided by the 
distance of the image, to the magnifying power of the te- 
lescope ; and giving the compasses to my friends, they gene- 
rally found that the proportional ends of them exactly fitted 
the points they had made on the card. All which experiments 
are only so many different ways of using the lamp-micro- 
meter. 
As to the mountains in Venus, I may venture to say that 
no eye, which is not considerably better than mine, or as- 
sisted by much better instruments, will ever get a sight of 
them ; though, from the analogy that obtains between the 
only two planetary globes we can compare, (the moon and 
the earth) there is little doubt but that this planet also has 
