60 
The Presidents Address. 
In the September number of ^ Silliman^s Journal/ Pro- 
fessor Smithy of Kenyon College, has furnished us with a 
better means of watching the growth of a plant under the 
microscope. He described a very useful invention for the 
purpose, which he called a growing slide, or trough, one of 
which, constructed by Mr. Suffolk, was shown to the Society, 
and is doubtless a cheap and useful contrivance. 
It consists of two pieces of thinnish glass, cemented 
together ; in one corner of the upper cover a small hole is 
bored, and through this a fresh supply of water is introduced 
without in any way disturbing the plant or living object 
under inspection. This can be constructed for a few pence. 
Mr. Beck has given us an improvement upon this : a descrip- 
tion of this gentleman^s may be found in our ^ Transactions.'' 
During the past year no improvement has been made in 
the construction of microscopic object-glasses. But we would 
call attention to the application of the single-front lens to 
the highest powers, in place of the triple combination usually 
employed by the different makers. A simple anterior lens 
transmits more light, gives clearer definition, with any desired 
extent of aperture, and, from its simplicity and comparati .^ 
freedom from errors of workmanship, is worthy of recom- 
mendation. The chromatic and spherical aberrations may be 
perfectly corrected in this form ; and Mr. Wenham informs 
me that there are now object-glasses existing, of various 
powers, having only a single-front lens, that will challenge 
comparison with the best of the usual form. 
It is suggested by Mr. Wenham, who has made practical 
investigations in the optical branch of Microscopy, that 
further improvements may be anticipated in the performance 
of object-glasses by discoveries connected with the quality of 
the glass employed. 
It is generally supposed that the dispersive power of flint 
glasses increases with its density : this, however, is found not 
to be the case. The best glass for the highest powers that 
has been made is a Swiss flint having a density of 3 "686. 
A few years back, Messrs. Chance made some beautiful clear 
and colourless flint glass not liable to tarnish, and which 
polished well, having a density of 3-867. Mr. Wenham 
availed himself of the opportunity and procured a quantity, 
but found, on trial, that the dispersive power was less than 
in the Swiss flint, at the same time that its refractive power 
was greater : these combined faults being in the wrong direc- 
tion, rendered the glass quite inferior for the construction of 
the higher powers. 
It thus became evident that some material had been added 
