18 
Mr W. Ritchie ou Radiant Heat. 
the surface of a heated body (see last Fig). Let us conceive 
the surface covered with a film of the molecules of caloric; 
Then^ it is obvious that those molecules which radiate in lines 
parallel to EC, have been darted off by the repulsive energy of 
these which are situated directly below them. Now, it is evi- 
dent, that the number of those repelling molecules, wilh be equal 
to those ranged along AB. Hence, it follows, that the quanti- 
ty of heat radiated from AC, in lines parallel to CE, will be 
equal to the quantity which would be radiated from AE in the 
Same direction, the temperature of AC and AE being the same. 
But AC is to AE as radius to the sine of -^ACE ; consequently, 
the flow of heat from AC in lines parallel to CE, is to the flow 
of heat from AC in lines perpendicular to AC, as the sine 
of ->::::ACE is to radius. 
The agreement of this conclusion with experiment, appears 
to be one of the most powerful arguments in support of the 
idio-repulsive theory, which we have endeavoured to illustrate 
and expand. 
Art. 111.— Account the Erection of' the Bell Rock Light- 
house. (With a Plate.) 
We SO rarely meet with minute details by scientific men of 
the operations of our great national works, that we gladly em- 
brace the present opportunity of giving our readers an account 
of one of the most diflicult undertakings of which the present 
age can boast. 
Our information is chiefly derived from Mr Stevenson’s large 
work, entitled, Account of the Bell Rock lighthouse, includ- 
ing the details of the erection and peculiar structure of that 
edifice.” This work extends to more than 500 pages of royal 
quarto, and is illustrated with 23 engravings. W e understand 
that only 240 copies were printed for sale : the circulation must 
therefore be very limited, and it must speedily become a scarce 
book. 
In an introductory chapter an account is given of the institu- 
tion of the Scottish Lighthouse Board in the year 1786, and 
