414 
PHILOSOPHICAL SOCIETY OF WASHINGTON. 
a uniform supply of heat, the curve of temperature as a function 
of the time shows for ordinary bodies a marked change of form 
as the material changes its state; this is also the,case with this 
glass when in crystalline state ; but when in a vitreous state the 
curve may be perfectly smooth from liquid to solid and back, and 
so the material has no true melting-point according to an}^ ordi¬ 
nary definition. [An extract from “The isomorphism and ther¬ 
mal properties of the feldspars,” Carnegie Institution, Publ. 
No. 31.] 
568th Meeting. April 25, 1903. 
The meeting was held in the rooms of the National Bureau 
of Standards, New Jersey avenue and B street S. E., through 
the courtesy of the Director of the Bureau and by vote of the 
Executive Committee of the Society. 
No formal papers were read, but the laboratories and shops 
were opened, and a great number of new instruments were ex¬ 
hibited and explained informally. Refreshments were served. 
About seventy persons were present. 
569th Meeting. May 9, 1903. 
President Gore in the chair. 
Forty persons present. 
The election and qualification of Messrs. J. R. Benton, P. 
Fireman, E. B. Rosa, A. H. Thiessen, and C. E. Yon Or- 
strand were announced. 
Mr. H. C. Bolton presented a paper, by invitation, on The 
genesis of hygrometers and anemometers, and detailed the suc¬ 
cessive steps in the development of these instruments. The first- 
named instrument was invented by Nicolas di Cusa, about 1450, 
and was based on absorption; the types based on the dewpoint 
did not appear till after 1800. The first anemometer was made 
in 1578. It is noteworthy that not only these instruments, but 
the thermometer (1595), the rain gauge (1639), and the barom¬ 
eter (1643), were all of Italian invention. [Not published.] 
Mr. E. E. Hayden then described, with the aid of lantern 
illustrations, The naval chronometer and time service. The navy 
