414 Letter OH Affairs m general. [APRIL, 



that the cylinder is constructed only of wood, covered with canvass (which 

 would be more pervious to the outward air than brick) ; and that the 

 exhaustion was extremely incomplete the barometer boing affected only 

 very slightly. But this result is precisely that which one would look for : 

 it will never be possible to accomplish the exhaustion in a sufficient degree ; 

 but SLT miles an hour, is very far short, indeed, of a hundred. One part, 

 however, of Mr. Vallance's scheme is rational and well imagined. He pro- 

 poses to come to London, and make an experiment, by constructing a 

 cylinder from London to Blackwall, with a view to carrying the heavy 

 goods, which are at present brought in waggons from the East and West- 

 India Docks. A work like this would come, in the way of expense, 

 within reasonable compass ; and, as regards the carriage of goods, the plan 

 would seem to be free from many difficulties which would attach to it in 

 the carrying of human beings. The transit, too, is so constant, that, if 

 Mr. Vallance's plan succeeded, there could be no doubt of his getting 

 immediate remuneration. 



The same paper contains a curious illustration of the uncertainty of 

 medical knowledge, in a paper read, or sent, by Dr. Magendie to the 

 Academie des Sciences. The subject is the exhibition of the concentrated 

 preparation of bark, the sulphate of quinine ; of which the doses given, a 

 little while back, in cases of ague and intermittent fever, were twenty-four 

 grains. Dr. Magendie finds, now, that exactly the same effect is produced 

 by the administering of two grains. This is odd ! But as the French 

 say, whenever there is a monstrous discrepancy between their statement 

 and yours c"est egal. 



There is no science, perhaps, that leads its votaries into so many jack- 

 a-lantern scrapes, and blunders, as "political economy." It hardly ever 

 happens that two men, even who fancy themselves on the same side, discuss 

 it, without presently finding that by a discipline as happy as that of the 

 allies in King John 



" Fiom north to south,'' 



like Austria and France, they 



" Shoot in each other's mouth!" 



In fact, the whole system of letting loose these '* fixed principles" or 

 abstract free action, in a state of society, in which all original principle, of 

 freedom of action, has long been sacrificed and abandoned, in favour of 

 vested interests, is as impracticable as it would he to talk of manoeuvring a 

 regiment of cavalry upon ground intersected at every ten yards by walls 

 and ditches; or of riding a steeple-chace, in the month of August, across 

 the counties of Buckingham or Bedford, without ruining the inhabitants, 

 because it so happens that \ve could perform the same exploit without 

 mischief on Dartmoor. Two discussions in the House of Commons, in tho 

 course of the last month which arose within four days of each other 

 involve a curious example of tiie danger of these sweeping maxims ; and of 

 the tendency which a principle in political economy has like the fabric 

 they call a "shot" silk to change its appearance entirely, as we change 

 the position in which we happen to look at it. Mr. Secretary Peel, on one 

 evening, in a conversation with the honourable member for Montrose, upon 

 the propriety of receiving certain petitions from labouring mechanics who 

 desired to have a tax upon machinery, laid down a principle as to the 

 force of which no economist will endure even to hear a doubt "that the 



