300 Tue Microscope. 
upper end of the objective and the one on the lower end of the 
body tube were made of the same size, every optician had a 
screw of his own so that there were almost as many sizes as 
there were manufacturing opticians. When an objective of one 
maker was to be used on the stand of another an adapter was 
necessary, one end of which must fit the screw on the body, the 
other that on the objective; and as many adapters were de- 
manded as the microscopist had objectives. Such a state of 
affairs must have been exceedingly inconvenient and annoying. 
The welcome change was due to the action of the Royal Micros- 
copical Society, which suggested that a certain sized screw be 
adopted by all manufacturers, which was finally done, and now 
the objectives of any reputable optician will fit the body screw 
of any stand. 
The inside diameter of the opening in the lower end of the 
body and the outside of the screw end of the objective, is about 
three-fourths of an inch. This is the Society screw, so called 
because first suggested by the Royal Microscopical Society of 
London. For most objectives as commonly made, it is amply 
sufficient, but for a few exceptional ones it has been found too 
small to allow them to exhibit all their good qualities. A few 
opticians make a few objectives whose angle of aperture is so 
great, and the diameter of their component lenses so large, that 
a special screw is demanded on the end of the body. This, at 
the suggestion of Dr. W. W. Butterfield of Indianapolis, is 
made about one and one-fourth inches in diameter. It is called 
after the inventor’s name ‘the Butterfield screw, and is to be 
found on first class American stands, which have almost every 
microscopical convenience, being placed above the Society screw 
so that, to use it, a part of the lower end of the body must be 
removed. It is not on the cheaper stands, and is not needed. 
Indeed it is not often needed anywhere. It is mentioned here 
only that the reader may know what the Butterfield screw is 
when he meets with the name in the microscopical literature of 
the day. The Society screw is an indispensable adjunct of every 
body tube, and is found on all American and English stands, 
however small and cheap they may be. And when the reader 
goes to the optician to select a stand, he will find it to his ad- 
vantage to recollect the size of the Society screw and its position. 
In this connection there is one rule to be remembered, and it 
