190 THe Microscope. 
factory records of what is seen under the microscope. To ef- 
fect this the only accurate and quick means is to photograph. 
Hence the student must not only be a good microscopist, but 
also understand the theory and practice of photography, an 
accomplishment which every engineer will find it useful to ac- 
quire.” 
Some limits are given for photographing and for selecting 
a microscope. The use of a condensing lense depends, it is said, 
upon the ability of the etched surface to reflect light. Thus 
hard steel reflects light so well that a condenser is not necessary, 
while in the case of pig, cast, or, wrought iron, its use is abso- 
lutely essential— Royal Microscopical Journal. 
ITEMS, 
EELS IN VINEGAR. 
WRITTEN BY GEO. ADAMS IN 1747. 
Dr. Powers observes that if vinegar, in which these eels 
abound, be moderately heated, they will die, and sink to the 
bottom. But cold does not hurt them, for after such vinegar 
had been exposed a whole night to the severest frost, and was 
frozen and thawed and frozen again, and so several times over, 
they were as brisk as ever. He also tells us that he put some 
vinegar full of. these eels into an essence glass and poured 
thereon about the same quantity of oil, which floating on the 
vinegar, all the eels would constantly creep up into the oil 
when the vinegar began to freeze, but when it thawed they as 
constantly returned to it again. 
To furnish yourself with minute eels, always ready for 
the microscope, boil a little flour and water till it comes to the 
consistence of such paste as the bookbinders and shoemakers 
use; expose it to the air in an open vessel, and to prevent its 
hardening or becoming mouldy on the surface, beat it well 
together whenever you find it tends that way; after a few days 
it will turn sour, and then if it be examined with attention you 
will find thousands of those eels on the surface thereof. To 
preserve them all the year you need only to put a little water 
to them if the paste grows dry, or a supply of other paste, 
