SCIENCE. 
283 
the Pleiades was made, in part, so that the distances of 
any pair of these stars might be used as a known celestial 
arc to be determined in terms of the screw revolution. 
Dr. Vogel, of Potsdam, determined the value of the screw 
of the Leipzig retractor by measuring the difference of 
declination between two stars with the micrometer, and 
afterwards using the divided declination circle of the 
equatorial to determine the whole arc. This method was 
improved in the determination of the value of the screw 
ot the Washington equatorial, by measuring with the 
micrometer the difference of declination ot two standard 
stars (« and c Orionis) a degree apart. In these last 
methods the value of the known arc in the sky depends 
upon our knowledge of the positions of its two terminal 
points. Dr. Winnecke, of Strassburg, has recently em- 
ployed an ingenious way, which is even more simple. 
The distance between some asteroid (whose orbit is well 
known) and any star near it, is measured on several nights, 
as the asteroid passes from north to south of the s f ar 
(let us say). Then, although the absolute position of 
the asteroid is not known, its daily motions are well de- 
termined, and the arc moved over may be used as a 
known distance from which the value ot the screw may 
be determined. 
The following complete list of asteroids (21 in all) dis- 
covered by the late Prof. James C. Watson, Director 
of the Washburn Observatory, Madison, Wis., has been 
compiled by the aid of the list of “ Minor Planets,” pub- 
lished by Mr. A. N. Skinner in the American Journal 
of Science and Arts, Vol. XVIII, Dec., 1879. All of these 
asteroids, with one exception, were discovered at the 
Ann Arbor Observatory, Michigan. Juewa was discov- 
ered at Peking, China, where Prof. Watson was in charge 
of one of the Transit of Venus parlies. 
Number. 
Name. 
Date of Discovery. 
79 
September 14, 1863. 
93 
August 24, 1867. 
94 
September 6, 1867. 
IOO 
Hecate 
July 11, 1868. 
IOI 
103 
104 
September 13, 1868. 
105 
September 16, 1868. 
106 
October 10, 1868. 
115 
August 6, 1871. 
Ir 9 
121 
May 12, 1872. 
128 
132 
133 
August 26, 1873. 
139 
October 10, 1874. 
150 
October 19, 1871;. 
l6l 
168 
174 
17s • 
October 1, 1877. 
The report of the Telegraphic Determination of 
Longitudes on the East Coast of South America, by 
Lieutenant Commanders F. M. Green, and C. H. 
Davis, and Lieutenant J. A. NORRIS, U.S. N., has been 
issued recently from the Hydrographic Office. This 
work embraces the meridians of Lisbon, Madeira, St. 1 
Vincent, Pernambuco, Bahia, Rio de Janeiro, Montevideo, 
Buenos Ayres and Para, and is designed to supplement 
the work done in 1877, under the direction of Lieutenant 
Commander Green, in the West Indies and Central 
America, by connecting important points in South Ame- 
rica, whose longitudes have always been exceedingly 
uncertain, with well-known places in Europe. 
Having made arrangements with the French Bureau 
des Longitudes to furnish the party with the difference of 
longitude between Lisbon and Paris, the work was begun 
in December, 1877, by connecting Lisbon, Portugal, with 
Funchal, Madeira, by means of an intervening station at 
Carcavellos. This “transmitting” station was found 
necessary in order to connect the submarine cables with 
the land lines ; a direct connection endangering the safe- 
ty of the cables. Partly by cables, and partly by the 
overland wires, the stations from Lisbon to Buenos 
Ayres were connected in the order named above, with 
the exception of a break between Pernambuco and Rio 
de Janeiro caused by a defect in the cable. These two 
stations were connected with Bahia, and Pernambuco 
with Para in 1879; and as the French Government had 
failed to communicate to the Hydrographic Office the 
longitude of Lisbon, it was determined to connect Lisbon 
with Greenwich, in order to make the chain complete. 
This last connection was effected by means of transmit- 
ting stations at Porthcurnow, Lands End, and Carcavel- 
los on the coast of Portugal. The reduction of com- 
parisons of the Lisbon and Greenwich clocks “ gives the 
somewhat startling result that the- longitude ot the ob- 
servatory at Lisbon, has, up to the present time, been in 
error more than two miles.” The American de’ermina- 
tion of the difference of longitude between these two 
places being 9 0 11" 10.2", while that heretofore accepted 
has been 9 0 9' 2.1". 
Of the instruments used, the Transit Instrument was ot 
what is known as the “ broken transit ” pattern (the eye- 
piece being at one end of the horizontal axis), especially 
designed for this work by Mr. J. A. Rogers, and fitted to 
be used as both transit and zenith-telescope. It was of 
2.5 in. aperture and 30 in. focal length — made by Kahler, 
It seems to have combined considerable steadiness with 
great portability, as it weighs in all but 125 lbs. In speak- 
ing of the performance of this instrument, the report 
says: “The results of the observations have demon- 
strated that the reversal of the axis is almost inevitably 
attended with a slight change of azimuth, and that a cor- 
rection must always be introduced for flexure of the axis,” 
and adds further on, that these effects “are probably un- 
avoidable in portable instruments of this pattern.” 
In the reductions, no correction has been applied for 
personal equation of the observers, either in noting tran- 
sits of stars, or in receiving the deflections of the gal- 
vanometer needle from the cables. After careful experi- 
ment, it was found that the correction, would be quite 
small, and in view of the uncertainty involved in its de- 
termination, it was decided to take no account of such 
j error, but to eliminate it, as far as possible, by placing one 
observer alternately east and west of the other, com- 
mencing at Lisbon. Advantage was taken of every op- 
portunity to make latitude determinations with the 
zenith-telescope, and the results in both latitude and 
longitude shc*w that nearly all of the stations occupied 
have been up to this time considerably in error. 
The spectrum of Hartwig’s comet has been observed 
I by Konkoly and Backhouse, and by Young in this coun- 
j try. It gives four bright lines, whose wave-lengths are 
j respectively 5609, 5492, 5169, and 4859 tenth meters, and 
| a faint continuous spectrum. W. C. W. 
Washington, D. C., November 30, 1880. 
SWIFT’S COMET. 
Swift’s comet is a faint object, and its distance from 
the sun is so great, never less than 1.102, and therefore 
always outside the earth's orbit, that no great changes of 
form are to be expected, such as we see in comets that 
pass near the sun. A. Hall. 
To the Editor of Science : 
Several interesting observations have been made by 
me of Swift’s latest comet. The last observation was 
made on the evening of November 26th, at 7.20 P.M.T., 
being then by estimation in about A. R. 2 hours 30 min- 
utes, north declination 53 degrees 45 minutes. It was 
| quite a conspicuous object in the 5-inch Newtonian Re- 
