a a i 
W. Ferrel—Relation between the Barometric Gradient, etc. 348 
order to demonstrate Dulong and Petit’s law, we must compare 
specific heats taken not at the same temperature, but at corres- 
ponding temperatures. This gradual increase to whic have 
called attention seems, then, to indicate a regularity in these cor- 
responding temperatures, rather than an irregularity in Dulong 
and Petit’s law. Taking our series of alkaline chlorides as an 
example, we may fairly suppose that their melting points (which 
have not been measured) are related to each other as the melt- 
ing points of the metals contained in them. Of these, lithium 
has the highest melting point, potassium next, then sodium, and 
rubidium the lowest. If the melting points are the correspond- 
ing temperatures for solids, and we determine — heats at 
one temperature, say at 20°, we shall have a value for lithium 
taken at a great distance from its proper temperature, one for 
potassium at a less distance, one for sodium still closer, and 
that for rubidium nearest of all. Then we should find that the 
substance having the lowest melting point possessed the high- 
est molecular heat, a result very naturally to be expected. It 
seems probable, therefore, that a careful investigation side by 
side of specific heats and melting points would lead to the dis- 
covery of some direct relation between these two sets of con- 
stants. For specific heat much new material is needed. For 
melting points there are but few valuable determinations 
extant. 
Art. XXXI— Relation between the Barometric Gradient and the 
Velocity of the Wind; by WM. FERREL. 
(Read before the Philosophical Society of Washington in June, and also the Amer- 
panty yf ytilnsrr cas a the parental of Science in August, 1874.) 
1. Let G= the barometric gradient in the direction in which it 
is the steepest, estimated by the amount of change 
in the mercurial column in the distance of 100 
miles ; 
v= the velocity of the wind per hour; 
*= the radius of curvature of the isobar or line of equal 
barometric pressure ; 
z= the ipatination of the direction of the wind to the 
isobar on the side of lowest pressure ; ae 
n= the earth’s hourly angular velocity of rotation in 
t of the radius; 
l= the latitude of the place; 
P = the barometric pressure of the atmosphere; 
P’= the value of P at the earth’s surface. 
