For factories and other places lighted with gas, care should be taken to ensure the escape of the products of combustion, either directly to the outside, or, when possible, by chimney ventilators, the action of which they would increase. These chimneys should be provided with registers to moderate their action according to the weather and the seasons.

Such are the terms in which General Morin describes his plan - really only a partial solution of the question, and a very incomplete one.

Nature, which often places the remedy close to the evil, in some cases inexpensively furnishes the means to cool the air. In ascending to the attics of dwelling-houses, the immoderate heat developed by the sun's rays is very perceptible, especially in cases where the roofs are covered with metallic substances. Now, the question is how to turn this heat to account for the introduction of pure air. In 1800, Dr. Anderson suggested the application of such a system. The mode of doing so is very simple. A ventilating chimney (see Fig. 13) is placed on the top of the building, to which abut side props, forming a double ceiling, and having communication by vents in the cornices. The fresh air coming from the cellars enters the room by hollow pillars of vertical props, according to circumstances; and at night, the natural heat of the sun not being available, artificial heat is employed. For museums and meeting-halls, Anderson proposed numerous chimneys having pierced glass frames on the southern side, and closed on the 3 other sides; the sun striking on the panes of glass would produce a draught commensurate with the intensity of the heat.

Regnault proposed a similar plan for the buildings of the Exhibition of 1855.

In Switzerland a system has been originated having great analogy with the proposals of Regnault. The inventor, Pradez, started from a very simple point of view. The negro, who is born in the torrid zone, has been endowed by nature with a woolly head of hair, which the sun strikes without reaching the cranium itself. As soon as the air contained in the hair is heated to a greater degree than that of the surrounding air, ventilation takes place of itself in a regular and natural manner; the negro, whose head is bare, is better protected against the rays of the sun than the European with his hat. Pradez has applied this observation to railway stations. By his plan, it is sufficient to protect the metallic roofs against the sun in the same manner that flowers are protected in hothouses against frost, viz. by straw bands of sufficient length and strength.

This is a very ingenious method, but like all those named, it can only be applied in a minority of instances.

Another method, recommended especially by Morin, is the imitation of the effect of rain; it is susceptible of being used almost directly to most edifices and dwellings. According to Morin, it would not require more than 1 1/2 cub. yd. of water per hour to moisten 100 sq. yd. of roofing, and to shelter them from the heat produced by solar radiation. Applied in the morning and during the heat of the day, it not only obviates the heating of roofs, but, as long as the temperature of the water is less than that of the air, it can maintain the interior walls at a temperature far inferior to the latter, and cools the air ascending to the attics. This method of watering being accidental, and only being required during some 60 days of the year, it is easy to see that even for a station as large as that of Orleans, which is 138 yd. by 28, the annual cost would be no more than 40/. sterling. It must be admitted, however, that this method, used in some places, is not to be recommended.

Fig. 13.

Cooling Air Part 6 40015

It is not only under the immediate roofs that the heat is intolerable during summer, the effects are visible on every floor; and if the heat be more sensibly felt under the roofage itself, it is quite clear that during the hot season there is a necessity for tempering the atmosphere throughout the house. The continual pouring of water on the roof of a house would have little effect upon the inhabitants of the first or ground floors. This refrigeration, on the contrary, would rather tend to arrest the course of the air from the attics, and would thus make atmospheric circulation less rapid. The constant dilapidation of the roof would also follow from a constant pouring of water upon it; it is hardly necessary to urge more by way of demonstration. The Roman architects employed this method in the amphitheatres; one vast cloth spread above the heads of the spectators was continually played upon by water jets. In our days some in-ventors have tried similar combinations; in some places blinds may be found on which a minute stream of water is playing.

To these contrivances, the strange name of hydraulic blinds has been given.

As pure air was sought to be drawn from subterranean localities, so also it was attempted to bring it from the skies; it has been taken from great elevations by means of high chimneys and steeples. At the Lariboisiere Hospital, the draught of air on the top of the tower is regulated by a mechanical ventilator fixed on the building. At Guy's Hospital, London, a similar method is used. The air drawn from the summit of the tower, by means of a chimney placed at its base, traverses the wards of the hospital, and is driven out by a second chimney situated in the vaults, producing a constant passage Of air in every apartment. However efficacious this method, it must be admitted that in summer the elevated strata of the atmosphere do not possess a temperature materially different from the lower air sufficient to mark the system as a success.

It is evident that these various methods of cooling the air may sometimes be simultaneously employed. This is what has been done in Russia by the engineer Derschau, the apparatus constructed by him offering an ingenious application of the two processes previously described. It is true that this application is expensive; but it was a saloon carriage for an empress, and in such a case expense is no object.