1878.] 
Notices of Boohs . 
547 
a tube, and exhausting by means of a mercurial air-pump at a 
red-heat. When this has been completed the tube is sealed up, 
and the last trace of mercury vapour, gas, sulphuric acid, and 
other impurities are absorbed by the charcoal, and in a few 
minutes the eleCtric spark refuses to pass through the vacuum. 
A very good vacuum may also be made by filling a tube with 
bromine vapour, and absorbing it by means of charcoal. Prof. 
Rijke gave a very interesting account of the historical instru- 
ments from Leyden, which included the first compound micro- 
scope made at Middleburg, by Hans and Zacharias Gaussen, 
before 1610 ; various mechanical contrivances of S’Gravesande 
for illustrating the velocities of falling bodies ; and lenses con- 
structed by Huyghens. 
The Mechanical SeCtion of the Conference was presided over 
by Mr. C. W. Siemens, and among the Vice-Presidents were 
General Morin, Director of the Conservatoire des Arts et Metiers, 
and M. Tresca, the Sub-DireCtor. The President’s Address and 
several of the earlier papers relate to the subject of measure- 
ments — linear, superficial, solid, eleCtrical — and of time. M. 
Tresca communicated a very important paper “ On the Flow of 
Solid Bodies,” embodying the results of many years of study 
and research ; Mr. Barnaby, Chief Constructor of the Navy, a 
lengthy and valuable paper “ On Naval Architecture and Mr. 
Thomas Stevenson described the more important improvements 
which have lately been made in lighthouses. 
The subjeCt-matter of this volume is most admirable, and 
the works cannot fail to be frequently consulted by men of 
Science. 
A Handbook of Practical Telegraphy. By R. S. Culley. 
Seventh Edition. London : Longmans and Co. 1878. 
This well-known work, which has been revised and considerably 
enlarged in this edition, contains an account of eleCtric telegraphy 
in all its forms. Commencing with the sources of electricity, 
the author passes on to a consideration of the laws of the current, 
static and dynamic induction, atmospheric electricity, and earth- 
currents. The construction of telegraph lines, the management 
of circuits, and the apparatus used for signalling are then dis- 
cussed ; a long section is given to submarine telegraphy; and 
recent inventions, including the telephone, are finally discussed. 
This work will undoubtedly continue to maintain the high 
position which it has so long enjoyed. 
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