SCIENCE. 
30 $ 
ASTRONOMY. 
swift's comet. 
Swift’s periodic comet, which has now become quite 
faint, was observed on December 10th and nth, with the 
26 in. equatorial of the Naval Observatory, and it is hoped 
that more observations will be obtained as soon as the 
moon has passed. On account of an elliptic motion, it 
has been slowly departing from the ephemer’s computed 
by Mr. Upton with parabolic elements and published in 
Vol. I, No. 21, of “Science.” 
The following is a continuation of Mr. Upton’s ephe- 
meris, which he has correc ed, however, from the most 
recent observations : 
Ephemeris. — Washington Mean Midnight. 
DATE. 
R. A 
Decl. 
H. 
M. 
s. 
1880, December 18 
5 
14 
44 
+ 38“ 5 3' 
“ “ 20 
5 
20 
40 
36 45-1 
22 
5 
25 
53 
35 29.9 
" ” 24 
5 
30 
35 
34 19-6 
“ “ 26 
34 
47 
33 H 
A NEW Astronomical Journal, Urania, edited by Dr. 
Ralph Copeland and Mr. J. L. E. Dreyer, is to appear 
early in January. It will be published in numbers of from 
16 to 24 quarto pages, as material can be accumulated. 
The names of the editors, Mr. Dreyer as a former assistant 
to Lord Rosse, and Dr. Copeland as Lord Lindsay’s as- 
sistant, are sufficient assurance that this will meet the 
want long felt in England and Ireland of a journal, pub- 
lished at frequent intervals, especially devoted to the in- 
terests of astronomers. 
Lieut. S. E. Tillman, of the Corps of Engineers, whose 
name is well known in connection with the American 
Transit of Venus Expedition to Tasmania, has been ap- 
pointed Professor of Chemistry, Mineralogy and Geology, 
at West Point, in the place of Professor H. L. Kendtick, 
who has voluntarily retired in order that this appointment 
might be made. Professor Tillman has had a very varied 
experience as an officer of engineers, his duties having 
led him to astronomical and geodetic work in the field 
and to geographical and geological explorations. The 
military academy may be congratulated upon having 
secured a valuable addition to its present strong academic 
staff. 
The volume of Washington Astronomical Observations 
for 1876, containing, in an appendix, the reports on the 
total solar eclipse of 1878, is expected, in a few days, 
from the Government printing office. 
Mr. S. C. Chandler, Jr., publishes, in Science Observer, 
a descrip ion of an instrument, the “ Almacantar,” which 
he has invented for determining time and latitude. The 
instrument is designed for the observation cf “ Equal 
Altitudes,” the principle upon which it is made being : 
that of Kater’s floating collimator. The Y’s, in which 
the pivots, rest are secured to opposite sides of a hollow 
iron rectangle which floats in a rectangular basin of mer- 
cury. The telescope can be clamped in altitude and the 
whole instrument rotated about a vertical axis. The 
float is allowed to seek its level, and thus the telescope 
will indicate equal altitudes on eitherside of the meridian. 
The probable error of a clock correction, as determined 
from a series of observations with this instrument, is about 
± 0.05 sec. W. C. W. 
P. S. — For notice of a new comet see page 297. 
To the Editor of Science : 
I observe what appears to be some errors in dates in 
the list of minor planets discovered by the late Prof. J. C. 
Watson, mentioned by your correspondent. 
( 1 33) Cyrene was discovered August 14, 1873. {Am- 
erican Journal of Science, III., vi, 296). 
(174) Phaedra was discovered August 8, 1877. ( Am- 
erican Journal of Science, III., xiv, 325). 
(175) Andromache was discovered September 2, 1877. 
{American Journal of Science, III., xiv, 325). 
He also discovered, October 20, 1857, the planet ob- 
served a few days before by Luther, and since named 
Aglaia; also, October 9, 1865, the planet seen by Peters 
a few days previously, and since named Io; also, July 29, 
1873, a planet which on account of cloudy weathe, 
eluded his subsequent observation. {American Journal 
of Science, III., vi, 296). 
A. WlNCHELL. 
University of Michigan, Ann Harbor, Dec. 11, 1880. 
MICROSCOPY. 
In the American Monthly'- Microscopical Journal for 
December, Dr. J. J. Woodward claims for Professor J. L. 
Riddell, M. D. of the United States, the priority in invent- 
ing at least two forms of Binocular Microscopes, since 
introduced by Beck of London, and Nachet of Paris. 
This communication of Dr. Woodward appears to prove 
beyond a doubt that to an American, Dr. Riddell, then of 
New Orleans, is due the credit of first demonstrating and 
publishing the optical principle, on which all the most suc- 
cessful binoculars, made prior to the present year, depend. 
He first showed that the cone of rays proceeding from a 
single objective may be so divided by means of reflecting 
prisms, placed as close behind the posterior combination of 
the objective as possible, that orthoscopic binocular vis'on 
can be obtained both with the simple and compound mic- 
roscope. 
While giving full credit to Dr. Riddell for all that is due 
to him, we think, in justice to Mr. Wenham, the fact 
should be admitted that he was the first to produce a bi- 
nocular arrangement for the microscope, so simple and per- 
fect in its form, as to render its general use possible. We 
once asked a London microscope maker, why the Stephen- 
son form of binocular was only' adopted by a very few 
microscopists, and were informed, in reply, that the ex- 
pense was great in constructing microscopes on this model, 
and on that account they were not popular. 
As we find from Dr. Woodward’s paper that the im- 
proved form of Dr. Riddell and that of Stephenson were 
practically alike, it may be that for this the reason neither 
received the attention anticipated. 
An interesting paper on Cercaria hyalocanda, by Herman 
C. Evarts, may be found in the same Journal. This larval 
form of a trematode .was observed to come from the com- 
mon pond snail {Physa heterostrophd) when placed in a 
shallow dish containing water. 
In form, the body when contracted was globular, and 
this form was maintained by the animal while actively' 
swimming about ; at rest it would extend its tail, and then 
assume a somewhat triangular form. 
They were sufficiently large to be seen by the naked eye, 
and were observed to encyst themselves, contracting during 
the process to a globular form, around which was secreted 
a glutinous mass. A few seconds after the cyst commenced 
to (orm, the tail detached itself and swam away. 
We are also indebted to this journal, for the descrip- 
tion of the following method of mounting opaque objects, 
contributed by Mr. A. II. Chester: — 
“ The object is first fastened to the slide, which is centered 
on the turn-table, by' means of a weak solution of gelatin, 
