162 
Rn 
INTERNATIONAL TRADE 
hand — are both available for a given product. Even when thus 
available, the data involve inference, and may call for qualifica- 
tion and explanation. They are after all indirect, not direct, 
and are less conclusive than observations or measurements which 
have in view an immediate comparison of the quantities of labor 
exerted for a given output. At all events, whether likely to be 
satisfactory or not, evidence of this indirect sort is not forthcoming. 
I may remark, by way of anticipation, that other evidence of the 
indirect type, indubitably significant, is available in abundance ; to 
this attention will be given in the next chapter. 
So far as concerns direct data, we are compelled to turn to 
scattered instances in which for one purpose or another information 
has been secured on the quantities of labor needed for producing 
given units of goods. To be pertinent for our inquiry, the infor- 
mation should relate, of course, not to one country alone, but to 
two or more ; that is, to one and the same commodity in the several 
countries. Such sporadic figures of this type as are available have 
usually been gathered for other problems than those of international 
trade. I proceed to adduce some data which have come to my 
attention. 
The Bureau of Mines of the United States Department of the 
Interior has been engaged for many years in an endeavor to check 
accidents in coal mines. This country has had a disgraceful posi- 
tion in this regard, standing lowest among all the advanced coun- 
tries in its record of accidents and fatalities. The Bureau of Mines, 
in the endeavor to bring out the large proportion of fatalities 
both to men employed and to tonnage mined, has collected 
figures of both kinds for various countries. It has thus enabled a 
comparison to be made of the relation between man power and 
physical output — the tons produced per year for each man 
employed. Figures are available showing how many tons of coal 
were brought to the pit’s mouth for each miner; and also how 
many tons for each worker of every kind (not only the underground 
men, but all employed about the mines). I give the figures for 
selected years: