il SOCIENCE.—AD VERTISEMENTS. 
Scientific Apparatus 
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ical and Optical Apparatus; Psychological Apparatus, 
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‘« Duty Free’’ Importations from all prominent 
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Correspondence requested. 
JAMES G. BIDDLE, 
Dealer, Manufacturer’s Agent and Importer, 
909 Drexel Building, PHILADELPHIA. 
Exhaustor 
Horsford’s Acid Phosphate. 
Overworked men and women, the 
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Descriptive pamphlet free on application to” 
Rumford Chemical Works, Providence, R. I. 
Beware of Substitutes and Imitations. 
For sale by all Druggists. 
NEW CATALOGUE. 
We have recently issued a new edition, revised and en- 
larged to 64 pages, of our catalogue of 
Books on Chemistry, Chemical 
Technology and Physics. 
It is arranged by subjects, and includes all the standard 
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A copy of this Catalogue will be sent free by mail to any 
address. 
D. Van Nostrand Company, 
Publishers and Importers of Scientific Books, 
23 Murray St. and 27 Warren St., New York. 
Dec. 1, 1896. Just Published. Sixth Edition of 
THE MICROSCOPE 438, "cRoscopi- 
CAL METHODS, 
By SIMON HENRY GAGE, Professor of Microscopy, His- 
tology and Embryology in Cornell University and the 
New York State Veterinary College, Ithaca, N. Y., U.S A. 
Sixth edition, rewritten, greatly enlarged, and illustrated 
by 165 figures in the text. Price, $1.50, postpaid. 
COMSTOCK PUBLISHING CO., Ithaca, N. Y. 
For 12 Cents 
I will mail a finely finished original photo, 
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15,000 Flint Stone Ancient Indian Relics. 100,000 Mineral 
and Fossil Specimens. Catalogue forstamp. 13th year. 
L. W. STILWELL, Deadwood, South Dak. 
SPECIAL NOTICE. 
Position desired in Engineering Offices, with 
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C. H. D., care of Science, 
66 FIFTH AVE., NEW YORK. 
HOUGH'S “AMERICAN WOODS” 
A publication illustrated by actwal specimens. 
WOODS FOR THE STEREOPTICON 
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VIEWS OF TYPICAL TREES 
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If you are interested in wood or trees in any way send for 
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