58 Account of the Erection of the Bell Rock Light-house. 
of France are placed, has devised and constructed, upon the 
most scientific principles, an apparatus with lenticular lenses^ 
which, from a lamp with four concentric wicks, transmits a most 
powerful light ; and that this apparatus is likely to be adopted 
as a permanent improvement on the coast of France, On this 
subject, it is not a little curious to remark, that, not many years 
since, when the Edystone Lighthouse came into the hands of the 
Trinity Board, the light had, till that period, been produced 
from two dozen of tallow candles, unaided by reflectors. 
Since this article went to press, we have seen the Report to 
the Instihde cf France on Mr Stevenson’s work by M, Navier, 
an engineer of great" promise, who is now constructing an exten- 
sive chain-bridge over the Seine at Paris. This report is dis- 
criminative, but, at the same time, highly laudatory to our 
countryman. The general character of the work is thus sum- 
med up : L’ouvrage de M. Stevenson ne laisse rien a desirer 
sur rhistoire et la description de cet important edifice. Get 
ecrit dont etre place au premier rang, parmi les livres utiles pu- 
blics par les ingenieurs, pour transmettre ii leurs successeurs la 
connaissance de precedes qu’ils ont employes.” 
Art. IV . — On the Principles and Practice of Warming and 
Ventilating Buildings. By Thomas Tredgold, Civil En- 
gineer, and Honorary Member of the Institution of Civil 
Engineers. 
In winter we require artificial heat, and during a short part 
of summer we seek for coolness, but at all times we need pure 
and wholesome air. These, however, are comforts which are 
not always to be commanded, and particularly where we desire 
to join economy with healthiness and, comfort. The principles 
concerned in the movement of invisible elastic fluids are seldom 
understood by those who engage in the management of ventila- 
tion ; and, in the still more recondite subject of heat, we too 
often find that the most absurd opinions are entertained. On 
