316 Scientific Intelligence. 
SCIENTIFIC INTELLIGENCE. 
I. CHEMISTRY AND PuHysics. 
1. Velocity of Light.—Lord Ratxzieu discusses the recent pa- 
per of Young and Forbes (Roy. Soc. Proc, May 17, 1881), in 
which it is maintained that bine light ‘travels in vacuo about 1:8 
per ie faster than red light, and asks the question: what is really 
determined by observations on the velocity of er t? Is the 
re of a single wave determined, or that of a group of waves? 
If the group velocity be denoted by 'U and the wave velocity by 
V, the relation between these velocities is explained by U= fit 
in which & is satnsed A de Sab sng to the wave length. Accord- 
ing to Young and Forbes, ith & and therefore U and V 
are different. A Snaploke knowledge of U, which can be obtained 
wave velocity. There aes be, therefore, a difference of two or 
three per cent between the pies velocity and the wave velocity. 
These considerations lead Lord Rayleigh to eae oa Ae a 
of Young and Forbes Nokes re, Aug. 25 psig neue 
one to observe the nod a sound wave in its 
passage through an organ is slotted along its en- 
tire side, is then placed in a Moreontel position with the slot be- 
neath and resting in a tro of wat he water thus forms a 
bie 18 
toes onductinsty 3 Metals for Heat and Hlecirivity. — 
In ee ee of a paper on this subject, Herr L. Lorenz 
discusses the theoretical laws of the cooling of metals when placed 
in ordinary air and extends his observations to the conduction 
of heat by metals in eset If T represents the absolute tem- 
perature, & and 2 the conductivity for heat and electricity 
respectively, he is led to the following expression: —=T x 
constant. According to his view there is Rucontinvity in the 
interior of every body and there are regions or sections along 
which free electricty can move without manifesting difference of 
