294 
P0PTJLA.11 SCIENCE KEYIETV. 
purcliase it. Unquestiona’bly it is an excellent little volume, mucli in- 
creased in size, and with a vast deal of new matter which is of the utmost 
importance. The author addresses it to the beginner, but we know that 
though it is unquestionably a book which is of the most infinite service to 
the unlearned observer, and which is specially wi’itten to supply his wants, 
very many experienced observers have it constantly on the table of the 
observatory as an invaluable companion. The present edition has its lunar 
map greatly improved, thanks to Mr. Birt’s kindness; its contents are 
enriched by the addition of 70 fresh sidereal objects, and the declinations 
now added to the Right Ascension Index will make it tout entier a most 
valuable companion. In Appendix I. the author has supplied, in condensed 
form, much information as to the most recent researches in Venus, giving a 
cut representing Bianchini’s diagram of the spots. Altogether the book is 
made most useful both to astronomers and amateur telescopists. 
WASHINGTON OBSERVATIONS EOR 1870.* 
A ppendix I. of these important observations contains Prof. Harkness’s 
^‘Report of the Difierence of Longitude between Washington and 
St. Louis.” The observations described in the Report were initiated by the 
United States Coast Survey, and the Observatory took part in them at the 
request of that institution, with the understanding that the observations at 
St. Louis should he made by Coast Survey officers, and those at Washington 
by Observatory officers ; and that at the conclusion of the campaign com- 
plete copies of the observations and reductions should be exchanged. The 
electro-magnetic apparatus employed at Washington was entirely automatic ; 
that employed at St. Louis was the ordinary Morse receiving magnet, 
sounder, and key, together with a break-circuit key. The difference of 
longitude finally deduced is thus expressed by Prof. Harkness (we invite 
special notice to the wording of the result): — ‘^The Observing-station at 
St. Louis, in the Washington University grounds, on St. Charles Street, 
between Seventeenth and Eighteenth Streets, is west of the centre of the- 
Dome of the United States Observatory at Washington, 
Oh. 52 m. 36-90 S. + 0.026 s.” 
Appendix II. relates to the observations of Encke's Comet, during its 
return in 1871, by Professors Hall and Harknese. These observations and 
their analysis are characterised by the care and abundance of labour usually 
found in American work of the kind. The results arrived at are thus 
summed up by Prof. Harkness : — “ (1) Encke’s Comet gives a carbon- 
spectrum; (2) from November 18 to December 2 the wave-length of the 
brightest part of the second band of the comet's spectrum was continually 
increasing; (3) no polarisation was detected in the light of the comet; 
(4) the mass of Encke’s comet is certainly not less than that of an asteroid ; 
(5) the density of the supposed resisting medium in space, as computed from 
* Reports of the Washington Observations for 1870:” Whashington 
Government Printing Office, 1872. 
