382 On a solar Calorimeter used in Egypt, etc. 



are equivalent to 3777 kgm. of work per minute or O'84 horse- 

 power. If we allow 1 6 per cent, for losses from all causes the 

 result is one horse-power received from the Sun by every 

 square metre of the area included in a great circle of the 

 Earth which is roughly I3OX io 12 sq. metres and this figure 

 in horse-power represents the working value of the Sun in its 

 relations to the Earth. Accepting the value of one horse- 

 power per sq. metre at the distance of the Earth we find by 

 simple arithmetic that the working value of I sq. metre of the 

 Sun's surface must be 45,000 horse-power. It follows that the 

 area of the Sun's surface which we may regard as hypothecated 

 to the Earth's heat service is no more than 2900 square kilo- 

 metres which would be contained in a circle of 60 kilometres 

 diameter and would subtend an angle of at most one-tenth of 

 a second. As over five hundred millions of such areas are 

 included in a great circle of the Sun, it is clear that the 

 maintenance of the Earth's heat is well assured. 



