Sailing and Steam-Vessels, 181 



holds, or between decks, to the galley-funnel, which, being 

 constantly heated, the circulation of the air from the ex- 

 tremity of the tube to the heated end becomes the natural 

 consequence ; and as the hold is hotter than the air in the 

 funnel after the fire is extinguished, the reverse will take place. 

 These tubes can with the utmost facility be placed so as to pre- 

 vent sparks or soot finding their way down, but which idea was 

 so prevalent some years back that they were discarded from 

 the navy. Tubes of two inches diameter of copper or iron 

 may be conducted along the sides into the after-hold, pump- 

 well, or any other part of the ship, with perfect security." 



Notwithstanding this favourable opinion, this method of ven- 

 tilating ships has not been extended, probably from the feel- 

 ing of insecurity against fire. In steam-ships, however, 

 where the powerful ascending current from the chimney-fun- 

 nel can always be had recourse to, such a method of ventila- 

 tion, with proper precautions to prevent danger from fire, may 

 come into more general use. A very general but obvious error 

 seems to have existed in the over estimation of the eifect of 

 tubes of two inches diameter, as already stated, to produce any 

 very decided iufluence on large masses of air. The very limit- 

 ed portion which can possibly pass from such tubes to the 

 galley-funnel in a sailing vessel, compared with the quantity of 

 air requisite to be renewed, must in most cases make this plan 

 of ventilating very ineffective. In a building which I lately 

 visited, where a similar plan was adopted for ventilating it, 

 the extracting air- tubes were only two inches in diameter for a 

 crowded room of ordinary dimensions, supposing the velocity of 

 the current moving oven at a quick rate, there being no provision 

 for the supply of fresh air, the effect of the abstraction of this 

 small portion must have been little in comparison with the 

 volume of air in process of vitiation. Hence, in any plan of 

 ventilation for extracting air by means of tubes, these must be 

 proportioned to the space ; and unless combined with fresh air 

 supplies, cannot be effective.* 



* One of the most useful instances of this mode of ventilation that I have observed, 

 was adopted several years ago at an extensive cotton-mill in the north of Scot- 

 land, where a direct communication was made on the different floors with the en- 

 gine-chimney, to suck out or extract impure air, but no provision for fresh air was 

 made, which is left to find its way through crevices or the windows when open. 



