284 
SCIENCE. 
flector, being fully as bright on that date as at any pre- 
vious observation, although its theoretical brightness is 
decreasing. It is a faint, diffused object, but to shew 
that it is within the range of quite moderate telescopes, I 
would say that I first picked it up on the evening of No- 
vember 5th, with a refractor of only two inches aperture. 
In my last observation two faint stars were seen shining 
through the comet. 
The comet’s position for the loth of December will be 
A. R. 4 hours 40 minutes, Dec. + 44 degrees 47 minutes. 
On December 14th it will be about 5 degrees south of 
Capella. William R. Brooks. 
Red House Observatory, Phelps, N. Y., 
November 30th, 1880. 
MICROSCOPY. 
Dr. Carpenter, the well-known English microscopist, oc- 
cupied the attention of the Royal Microscopical Society, 
on the 6th instant, by describing the “Student Micro- 
scope,” recently designed by Mr. George Wale, of New 
Jersey. The instrument in question was highly com' 
mended for its efficiency, and English opticians were 
advised to consider the practical improvements it suggests. 
Mr. James Swift exhibited and described an improved 
form of Calotte diaphragm, consisting of a series of small 
circular apertures, to be applied above the achromatic 
condenser immediately beneath the object, and on a level 
with the surface of the stage. 
A binocular eye-piece, by Professor E. Abbe, was de- 
scribed as consisting of two uncemented prisms (together 
forming a thick plate of glass) in the direct tube ; the ad- 
jacent diagonal surfaces of the prisms being both cut at 
the calculated angle of 38° 5', which angle was computed to 
allow precisely one-half of the light to be transmitted, and 
to reflect the other half ; the latter half fell upon a total re- 
flecting prism, whence the rays emerged through the 
diagonal tube to the left eye. Another point was the 
mechanism by which the diagonal tube attached to the 
direct tube by a box-fitting, was moved to accommodate 
the width of different observer’s eyes, a screw motion 
causing the tube, with eye-pieces above and reflecting 
prism below, to travel smoothly nearer to or further from 
the direct and stationary tube. 
The application of the eye-piece to the left tube at such 
a distance as to compensate for the extra distance travelled 
by the pencil of light, and thus render the images seen by 
both eyes of equal magnitude. 
Lastly, the application of two semi-circular caps, one 
over either eye-piece ; in one symmetrical position of these 
apertures the effect produced was pseudoscopic vision, by 
another arrangement of them stereoscopic vision was ob- 
tained. 
This form of binocular is said to be specially appli- 
cable to the short tubes of Continental microscopes and 
some of American make, 
A new fluid for writing the names of objects on glass 
slides is sold by Mr. Browning, of London. It is more active 
than hydrofluoric acid, and has an immediate action on the 
surface of glass. 
Dr. Gunther, of Berlin, has made photographs of Frus- 
tulia Saxonica. These and a micro-photograph by Mr. S. 
Wells, of Boston, were compared with the photograph by 
Dr. Woodward, produced in 1875. The latter showed no 
trace of beaded resolutions, whereas both the former showed 
the resolutions remarkably well. Mr. Mayall asks if Dr. 
Woodward still maintains his opinion of the unreality of 
the longitudinal lines. 
Mr. Crisp mentions that Professor Abbe has found great 
advantage in mounting diatoms in monobromide of naph- 
thaline, by which they were rendered far more visible than 
when mounted on Canada balsam. 
BOOKS RECEIVED. 
The Naturalist’s Directory for 1880. Edited 
by Samuel E. Cassino, 299 Washington street, 
Boston. May, 1880. 
This useful work will be welcome in scientific circles ; 
it contains the names, addresses, special departments of 
Study, of Naturalists, Chemists, Physicists, Astronomers, 
etc., etc., etc. It also gives a list of scientific societies, 
of scientific periodicals, and the titles of scientific books 
published in America from July 1, 1879 to October 1, 
1880. 
The arrangement of the names in this edition of the 
directory is by States, and was adopted after repeated 
requests, though not, as the publisher admits, without 
misgivings on his part as to the convenience of the 
list thus arranged. On this point we are glad to notice 
that what we consider to be an error is acknowledged, 
and that in future the alphabetical order will be resumed. 
For our purposes the directory thus arranged is almost 
useless, as the loss of time in searching 45 separate lists 
for an address, is a great drawback to the use of the 
work. 
We are also at a loss to know on what principle the 
list has been constructed, as the omission of the names 
of well-known scientific men is quite incomprehensible ; 
as examples we fail to notice Professor John Le Conte, of 
California; Professor W. H. Brewer, of Yale; Professor 
Jas. D. Dana, of Yale; Professor Simon Newcomb, of 
Washington ; Col. J. J. Woodward, M. D., Washington ; 
Professor Asaph Hall; Professor Julius E. Hilgard, 
Washington ; Professor C. Y. Young, of Princeton ; Pro- 
fessor C. F. Chandler, of New York City; Professor 
Henry Draper, of New York City; and Professor Jno. 
W. Draper, of Hastings-on-Hudson, or Mr. Edison. We 
have had no time to make a systematic search for omis- 
sions, but the above names which are household words 
in scientific circles do not appear. 
As we find some of these names have already appeared 
in previous editions, the present omission would not 
appear to be altogether accidental. 
As this directory is the only one of its kind published, 
we suppose these errors will not effect its sale, but we 
regret that a more perfect work was not produced. 
Since writing the above notice, we have heard from the 
publishers of the Directory ; they state that the arrange- 
ment of the work is acceptable to a majority of the sub- 
scribers, and that the cause of the omission of names was 
due to their failure to receive responses to printed cir- 
culars which were forwarded to all known scientists”. 
The readers of this journal must be familiar with the 
efforts we have made to secure a perfect register of the 
scientific men of the United States. Our intention in 
this respect was also made known by an editorial notice in 
the New York Titnes, and in the Medical Record of last 
week. 
The Titnes pointed out the value of such a perfect list, 
and the little trouble it entailed on scientific men. So 
far the response to our appeal has been very partial. 
We therefore again request those who have hitherto 
failed to forward their names and addresses, with special- 
ity of study, to do so at once, and if the heads of Uni- 
versities an> I Colleges would make up lists, considerable 
help would be rendered. 
We also suggest that those interested in scientific pur- 
suits make up lists of scientific men in their neighbor- 
hood, and of amateurs following a particular line of 
scientific investigation. 
As we stated lists of names will be forwarded to the 
Smithsonian Institution, and Messrs. Cassino and others 
will have the full benefit of it for future use. 
