EEYIEWS. 
295 
the observed retardation of Encke’s Comet, is such that it would support a 
column of mercury somewhere between and ~~ of an inch high; (6) 
there is some probability that the electric currents which give rise to 
auroras are propagated in a medium which pervades all space, and that the- 
spectrum of the aurora is in reality the spectrum of that medium ; (7) it is 
not improbable that the tails of all large comets will be found to give- 
spectra similar to that of the aurora, although additional lines may be 
present.” It will be seen from this that the discussions in the body of the 
paper are of great interest. 
hlEMOIR OF THE FOUNDESTG AND PROGRESS OF THE 
UNITED STATES NAVAL OBSERVATORY.* 
HIS is an exceedingly interesting account of the events which have 
happened since 1810, when proposals were first made for a Government 
observatory in the United States, to 1842, when the Washington Observa- 
tory was fdunded, and thence to the present time, with a general description 
of the instruments in use, &c. In concluding this memoir, its author. 
Prof. Nourse, remarks with great justice, that the position now accorded to 
the U. S. Naval Observatory, by the free tributes of scientific men in the 
Old World, as well as at home, is not without honour to America, and this- 
notwithstanding the comparatively recent founding of the institution, and 
the as yet limited appropriations sustaining it.” We regret, however, to- 
see that the somewhat excessive respect with which Americans are too> 
apt to treat European science (to which American science is certainly not 
inferior), has led Prof. Nourse into the mistake of quoting measures which 
had been proposed within the Astronomical Society when his paper was 
written, but have since been rejected with something resembling contempt 
by an all but unanimous vote of the Council of that body. 
PAPERS ON THE TRANSIT OF VENUS IN 1874.f 
T hese papers contain the discussion of the circumstances of the approach- 
ing transit, by Professors Newcomb, Coffin, and others. The results 
are indicated in our summary of Astronomy. Very beautiful and exact 
charts illustrate Part II. 
W E have before us two books, the one on electricity and magnetism, the- 
other on general natural philosophy, which are as different in point 
of value as it is possible to conceive. That by Prof. E. Jenkin is, without 
* ^‘Washington Observations for 1871, Appendix IV.:” Washington. 
Government Printing Office, 1873. 
t Washington Government Printing Office, 1872. 
X “Electricity and Magnetism,” by Fleeming Jenkin, F.R.S., Prof, of 
Engineering in the University of Edinburgh. London : Longmans, 1873. 
PHYSICAL SCIENCE.! 
