ON CONSTRUCTING STANDS OF MICROSCOPES. 161 



constructions. First, then, it has been said, that the 

 double motion of a ball and socket joint is of a most un- 

 manageable nature, and that a cradle joint is a true, 

 regular, and far superior movement : this I admit, and 

 should say, that if a telescope had, by means of a ball 

 and socket, to follow the motion of a star, no motion 

 could be more unappropriate and detestable ; but in a 

 microscope it happens always to be a fixture, and when 

 clamped tight by means of a pinching-screw, is as steady 

 as a rock. 



This observation may appear very unnecessary to my 

 readers in general ; but I have met with individuals of 

 such obtuse understandings, that they cannot be brought 

 to comprehend that a telescope performs a part of its 

 motion by means of its cradle joint, whereas that of a 

 microscope is the result of a traversing motion in its arm, 

 combined with a rotatory one on the top of the bar, and 

 therefore has nothing to do with that on the head of the 

 stand, be it what it may, which is always a pro tempore 

 fixture. 



Again, it has been said, that by giving the motions and 

 adjustments to the optical part, it is rendered much less 

 steady than it might be under other circumstances ; that 

 it is like mounting a telescope on a mop-stick : that 

 immobility is of most virtual importance for observa- 

 tion, &c. I answer, that by making the work sufficiently 

 strong and solid, and the optical part no larger or longer 

 than is necessary, the instrument is rendered abundantly 

 steady, and free from tremor even with its highest powers. 



M 



