Ciur. VIII.

BRITAIN.

613

Fig. 577.

TRANSVERSE SECTION OP PRISON.

respectively in a grating placed close under the arched ceiling of each cell, into which acurrent of air is thus introduced.

It is very difficult to lay down a plan for the ventilation of public buildings, particularlyas the sites and uses present so much variety : the various improvements that have beensuggested on this subject for deep mines, and in some instances carried into effect, haveturned the attention of the architect and civil engineer to adopt some method that shall insurea stream of pure and properly tempered air to follow the exhaustion that takes place in ourchurches, halls of assembly, or wherever great masses of people meet together and areconfined for any length of time; in a future part of the work the subject will be more fullytreated. It does not appear that attempts were made to renovate the atmosphere ofthe cells of our prisons until practised here: much has been judiciously effected, but,with all the precautions hitherto adopted, none have yet been found to answer perfectly.Temperature and pressure exert so many influences, and, in conjunction with radiationand evaporation, so change the properties of the air, that it is exceedingly difficult toconstruct by means of pipes, valves, or machinery, contrivances that shall counteract ormitigate them. The section of the windows represents by the arrow-heads the currentthat the air takes in its passage, and the escape of the foul air to the outside of the cell:the handle attached to the valve that admits the warm air is at the prisoner's command ; hecan consequently introduce the desired quantity at pleasure; the windows are so formedthat thorough ventilation is obtained.

The window frames are formed of iron: their plan shows the manner in which they

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