$38 General Notes. [ December, 
of copies of that division as corrected are ruled, and the one se- 
lected which corresponds most nearly with the computed correc- 
tion. A similar process is applied to each subdivision, and finally 
these subdivisions are compared among themselves, and the one 
selected which is nearest the mean of the whole number. Thus 
the əy of a standard yard, and the z4y of a standard metre, have 
been obtained with a certainty not believed to have been secured 
before. The standard centimetre thus produced by Prof. Rogers 
was submitted to the Congress for the use of members who 
might desire to determine the value of the divisions of their 
micrometers in terms of the Coast Survey standard. 
Prof. J. D. Hyatt, of New York, gave a very interesting address 
on “The Sting of the Honey-bee,” illustrated by a large number 
of diagrams. His paper, with its illustrations, will be published 
in the forthcoming number of the new quarterly. 
“On the Construction of Oculars,’ by Wm. H. Seaman, of 
Washington. The discrepancies in published statements in regard 
to oculars, led the author to make a full series of measurements 
of the parts of eighteen oculars by English and Continental | 
makers, and to present the results in a tabular form. By inspect- 
ing the table it appears that the common ratio between the foca 
lengths of eye lens and field lens is 4, in one instance it is 4, and in 
one of older construction 4. The only general principle in 
regard to the interval separating the lenses is, that it shall be less 
than the solar focus of the field lens; and when in the deeper 
oculars, and those which are orthoscopic, it seems to exceed this 
limit, it must be remembered that in connection with the objective 
the ocular receives diverging rays, and for such, its focus 15 
beyond the solar focus. It may also be noticed that but a small 
part of the diameter of the eye lens is actually used in the lower 
powers. | 
Prof. J. E. Smith made some remarks on “ Micrometer 
Rulings,” repeating his claim, formerly published, as the first to 
have. resolved Nobert’s 19th band, by reflected light. He also 
expressed the belief that he had resolved by reflected though not 
by transmitted light bands of ys/ggeth inch ruled, or attempted 
to be ruled, by Rogers. - 
:“ A New Turn-table ” was exhibited and described by John W. 
Sidle, of Philadelphia. This table is self-centering by the Cox 
_ method, having jaws that press diagonally toward the center of 
the slide. Instead of the screw movement of the original form, 
or the lever or scroll screw of later modifications, the jaws are 
mounted near the edges of two small circular discs which are set 
into the main plate or table, on opposite sides of the center, and 
= which by revolving simultaneously change the distance of the 
jaws from the center of the table. The mechanism seemed un- — 
likely to get out of order, and a very steady and prompt motion 
