vB SCIENCE—ADVERTISEMENTS 
Important New Books 
Principia Mathematica by Atrrep NortH Wurrensap, Sc.D., F.R.S., 
Trinity College, Cambridge, and Brerrranp Roussett, M.A., F.R.S., 
Trinity College. Vol. I, $8.00 net. Vol. II, $10.00 net. (To take the 
place of Russell’s Principles of Mathematics. ) 
Lectures on the Differential Geometry of Curves and Sur- 
faces by A. R. Forsytx, Sc.D., LL.D., Math.D., F.R.S., University of 
Cambridge. $7.00 net. 
An Elementary Treatise on Statics by 8. L. Lonry, M.A. $4.00 net. 
Examples in Applied Mechanics and Elementary Theory of 
Structures by Cuartes E. Ines, M.A., A.M.I.C.E., King’s College, 
Cambridge. 75 cents net. 
A New Law of Thought and Its Logical Bearings by E. E. Con- 
STANCE JoNES. Preface by Professor Stout. 65 cents net. 
2,g.and6West GP, PUTNAM’S SONS = 27 “3ty ctrect 
Educational Department 
NEW YORK CITY 
LEITZ’ NEW MICROSCOPE 
“STAND II L” 
With continuous side fine adjustment. 
This is the fine adjustment which has made the New Leitz 
Microscope Stands so popular. Characteristic of this fine adjust- 
ment is its high degree of sensitiveness, at the same time 
possessing great stability. It also provides a device for absolute 
protection of objectives, as well as specimens, against 
injury. This most convenient way of focusing the microscope is 
a very important item, not to be overlooked. 
Our traveling microscopes, bearing this same fine adjustment, 
have withstood many years of hard usage to which they 
are naturally subjected ; sufficient proof of stability. 
The fact that stands with this type of fine adjustment have here- 
tofore been considerably high in price, may explain the reason for 
some institutions not having placed them in their laboratories. 
That therefore the introduction of our moderate priced 
‘¢ Stand II L’’ has found interest is sufficiently proven by the 
ever increasing demand. 
Send for literature. 
New York 
30 East 18th Street 
