245 
tained by drawing out glass threads and determining their tensile strength 
by the method already described. 'That the increase in the case of glass 
threads was due in 
part only to the “skin 
effect’? was indicated 
by the fact that 
the tensile strength 
measurements for 
threads of different 
Sizes were made more 
nearly uniform by 
carefully annealing 
the threads. This was 
done by hanging the 
threads in a verti- 
eal iron tube with a 
small weight at- 
tached to the lower 
end of each thread 
to keep it straight. 
The entire tube was 
then brought to a 
temperature slightly 
below the melting 
point of glass and 
maintained at that 
temperature for one 
hour, after which it was allowed to cool slowly in the asbestos jacket sur- 
rounding it. ; 
An attempt was made to anneal the gelatine threads by hanging them 
in a moist atmosphere in an enameling oven. Various oven temperatures 
were tried with little permanent effect on the threads. The author in- 
clines to the view that the “skin effect” does not account for the larger 
values of the tensile strength shown by the finer gelatine threads, but that 
it is due chiefly to the cause already suggested—the greater uniformity in 
the finer threads. 
