45 
Assuming that the friction between two sections of the 
wire is proportional to their relative velocity, a hypothesis 
which accounts well for certain phenomena in sound, 
I worked out its effect in this case, but the result failed to 
account for the facts. This should not be surprising, for 
though this assumption may be true or nearly so for small 
relative velocities, it may well fail here when they are large. 
The discrepancy may perhaps be attributed to the fact that 
a strain which a wire will stand a short time, will ultimately 
break it, and possibly in part to want of rigidity in the 
. supports of the upper clamp, both of which would favour 
the heavy weight. 
I think we may conclude from the above considerations 
and rough experiments, 
1st. That if any physical cause increase the tenacity of 
of wire, but increase the product of its elasticity and linear 
density in a more than duplicate ratio, it will render it more 
liable to break under a blow. 
2nd. That the breaking of wire under a blow depends 
intimately on the length of the wire, its support, and the 
method of applying the blow. 
3rd. That in cases such as surges on chains, etc., the effect 
depends more on the velocity than on the momentum or vis 
viva of the surge. 
4th. That it is very rash to generalize from observations 
on the breaking of structures by a blow in one case to 
others even nearly allied, without carefully considering all 
the details. 
“ Observations upon the National Characteristics of 
Skulls,” by S. M. Bradley, F.R.C.S., Lecturer on Compara- 
tive Anatomy, Royal School of Anatomy and Surgery, 
Manchester. Communicated by Professor H. E. Roscoe, 
F.R.S. 
The object of this paper was to show that the classification 
at present in vogue, which arranges the crania of different 
nations into four groups, viz., 1, dolicocephalic-orthognatliic; 
2, dolicocephalic-prognathic ; 3, brachycephalic-orthogna- 
