40 SCIENTIFIC HOOKS FUBLISHEU BY 
Saeltzer’s Acoustics. 
12mo. Cloth. $2.00. 
TREATISE ON ACOUSTICS in Connection with Ventilation. 
With a new theory based on an important discovery, of facilitat- 
ing elear and intelligible sound in any building. By Alexanber 
Saeltzer. 
“ A practical and very sound treatise on a subject of great importance to 
architects, and one to which there has hitherto been entirly too littlo attention 
paid. The author’s theory is, that, by bestowing proper care npon the point 
of Acoustics, the requisite Ventilation will be obtained, and vice versa.— 
Brooklyn Union. 
Myer’s Manual of Signals. 
.New Edition. Enlarged. 
12mo. 48 Plates full Eoan. $5.00. 
MANUAL OF SIGNALS, for the Use of Signal Officers in tho 
Field, and for Military and Naval Students, Military Schools, 
etc. A new edition, enlarged and illustrated. By Brig.-Gen. 
Albert J. Myeh, Chief Signal Officer of the Army, Colonel of 
the Signal Corps during the War of the Rebellion. 
Larrabee’s Secret Letter and 
Telegraph Code. 
18mo. Cloth. $1.00. 
CIPHER AND SECRET LETTER AND TELEGRAPHIC 
CODE, with Hogg’s Improvements. The most perfect secret 
Code ever invented or discovered. Impossible to read without 
tho Key. Invaluable for Secret, Military, Naval, and Diplo 
matie Service, as well as for Brokers, Bankers, and Merchants. 
By C. S. Larrabee, the original inventor of tho scheme.