li SCIENCE.—AD VERTISEMENTS. 
Scientific Apparatus 
““Bowboin’? X-RAY Focus TuBE. 
My Specialties Are: 
«© W-S’’ X-Ray Apparatus; Weston Ammeters, Volt- 
meters and Wattmeters; ‘‘Chlorid Accumulator’’ Stor- 
age Batteries; Electrical Measuring Instruments; Phys- 
ical and Optical Apparatus; Pyschological Apparatus, 
ete. 
‘‘ Duty Free’’ Importations from all prominent 
European makers. 
Correspondence requested. 
JAMES G. BIDDLE, 
Dealer, Manufacturer’s Agent and Importer, 
909 Drexel Building, PHILADELPHIA. 
Clark University July:- 
Summer School, 2¢ IQ-3Ie 
WORCESTER, MASS. 
Psychology, Biology, Pedagogy and Anthropology 
NATURE STUDY A LEADING FEATURE. 
The following Instructors give daily lectures or demonstra- 
tions :— 
G. STANLEY HALL, Ph.D., LL.D., President of the Univer- 
sity and Professor of Psychology; CLIFTON FP. HODGE, Ph.D., 
Assistant Professor of Physiology and Neurology; Ep- 
MUND C. SANFORD, Ph. D., Assistant Professor of F’sychol- 
ogy; WILLIAM H. BuURNHAM, Ph.D., Instructor in Peda- 
gogy; ALEXANDER F. CHAMBERLAIN, Ph. D., Lecturer in 
Anthropology; ADOLF MEYER, M.D., Docent in Psychiatry; 
COLIN C. STEWART, Fellow in Physiology. 
For circular and particulars, address 
LOUIS N. WILSON, Clerk. 
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 
books in Chemical and Physical Science, as well as the re- 
cent literature up to date. 
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. 
Delicious 
Drink 
with water and sugar only, makes a 
delicious, healthful and invigorating 
drink. 
Allays the thirst, aids digestion, and 
relieves the lassitude so common in 
midsummer. 
Dr. M. H. Henry, New Vork, says: ‘‘When 
completely tired out by prolonged wakefulness 
and overwork, it is of the greatest value to me. 
As a beverage it possesses charms beyond any- 
thing I know of in the form of medicine.”’ 
Descriptive pamphlet free. 
Rumiord Chemical Works, Providence, R. I. 
Beware of Substitutes and Imitations. 
RARE MINERALS. 
THAUMASITE, from Paterson, N. J., a sulphate, silicate and 
carbonate of calcium, pure white, 25c. 
EKDEMITE, bright yellow on red wulfenite, Arizona, 50c. 
ANE ARSENIC, Japan, 44 to 34-inch ersytallized balls, 
Cc, 35c. 
Collections for Schools. 
ALPHA COLLECTION, twenty-five specimens in trays, con- 
tained in a neat wooden box and accompanied by a 46- 
page guide book (XIII., Guide for Science Teaching, Bos- 
ton Society of Natural History), Price, complete, $1.00. 
CABINET COLLECTIONS, 100 specimens, small size, $5.00. 
100 specimens, large size, $10.00. These specimens are 
each accompanied by a label giving name, system of 
crystallization, chemical formula, and locality, and make 
a good working collection for a student. 
EXCELSIOR COLLECTION for high schools and colleges. 
200 specimens, nicely mounted on wooden blocks, with 
beveled fronts for receiving labels. Price, packed, 
$100.00. School Bulletin just out. 
Loose Crystals. 
Small packages of free crystals for crystallographic study 
may be sent for inspection by mail at small cost. Ap- 
proval boxes of cabinet specimens by express or freight. 
ROY HOPPING, 
MINERAL DEALER, 
504-506 Liberty Building, 
Liberty and Greenwich Sts. NEW YORK. 
