34 



UNDULATORY FORCES. HEAT. [VENTILATION or CHURCHES, ETC. 



enters the vowel on ono side of the card, whilst another 

 loaves it on the other side. These currents will bo better 

 observed, by holding a little smouldering brown paper 



iu';ir the nock of the ves- 

 sel, when smoke will bo 

 seen to enter, and to leave 

 by the opposite openings. 

 Witt such an arrangement, 

 the candle may be made 

 to bum any length of time ; 

 because a continual supply 

 of cold air is admitted, and 

 the carbonic acid gas is re- 

 moved. 



By dividing a pipe, running from any opening in a 

 ceiling, into two parts, in a similar manner as is done by 

 the card in the neck of the glass jar, or by inserting 

 within each other two cylinders, separated by a distance 

 of a few inches, and placing them in an orifice at the top 

 of a room, a system of ventilation may be tolerably 

 carried out. This principle was adopted by Mr. James 

 Kite, about twenty years ago, for the purpose of venti- 

 lating ships' cabins. His arrangement consisted of an 

 iron pipe, divided into two parts by means of a slip of 

 metal. Mr. McKinnell, of Glasgow, has improved on 

 this, and has been 'very successful in hia attempts at 

 ventilating many public buildings. The annexed en- 

 gravings illustrate both of these inventions. 



Fig. 15. Fig 16. 



Klt' Ventilator. McKinnell's Yentil>tor. 



The arrows show the direction of the currents of air. 

 In this, and similar modes of ventilation, an entire 

 change of the air of the apartment is never produced ; 

 because the. supply of fresh, and the escape of foul air, 

 are never carried on to sufficient extent for that end. 

 Dilution alone is effected, so that a considerable amount 

 of impurity necessarily remains. 



A very ingenious, but complicated plan, was adopted 

 some years ago, by Dr. Reid, in the ventilation of the 

 houses of parliament. Arrangements having been con- 

 structed for wanning the air when necessary, it was 

 allowed to enter through an immense number of small 

 holes in the floor of the house ; the upward draught 

 being produced by a tall ventilator, fixed on the roof. 

 This, whilst highly scientific iu plan, was unfortunately 

 not successful in practice. Of course every one present 

 was necessarily in a continuous draught of air ; and the 

 result of this, in most instances, is injurious to health, 

 Mid productive of cold, &c. Few are aware of the differ- 

 ence of being exposed to either an extreme high or low 

 temperature in still air, and in a current of air of the 

 same temperature. In the latter case, rapid evaporation 

 takes place, and consequent cold is produced. Thus, in 

 the Arctic regions, the most intense cold may easily be 

 sustained, provided no breeze is blowing ; but the same 

 would be productive of the greatest inconvenience, and 

 possibly of death, during a strong wind. Modifications 

 of Dr. Reid's plan are now often adopted in many 

 large buildings, such as churches, concert-rooms, <fco. 

 Air is admitted through openings or grids in the floor ; 

 and a number of concealed openings are made in the 

 roof, through which the foul air makes its escape. The 

 burning of gas materially assists this process of ventila- 

 tion, by causing a continual upward current of hot air. 

 The introduction of "sunlights," which are always placed 

 in the ceilings of rooms, also aids in promoting ventilation. 



Wo may hero inquire into the cause of those down- 

 wan! cold draughts which frequently produce so much 

 unpleasantness in churches, <bc. ; and which, from the 

 ignorance of those in charge of the ventilating arrange- 

 ments, are often ascribed to wrong causes. In nearly 

 every instance, those downward draughts are chiefly 

 found at the sides of a building; and in the case of 

 churches, they are mostly observed near the walls and 

 windows; and despite all attempts to make the latter 

 air-tight, still these draughts will be felt. Their cause is 

 easily explained. The hot air, rising in the centre of the 

 building, impinges on the roof, and escapes, if suitable 

 openings are made for that purpose. At the same time, 

 the walls and windows being of a lower temperature than 

 the air, cool it, and thus the air descends to the floor of 

 the church, being denser than the central rising volume. 

 If, however, the glass of the windows is covered by 

 means of calico, blinds of any sort, or a thick coat of 

 paint, its conducting power is lessened and the down- 

 ward draught speedily diminished. Hence the A 

 of double windows, which, by enclosing a body of air be- 

 tween them, prevent the cooling effect which wo here 

 speak of. 



It is much more difficult to overcome the cooling effect 

 of the walls, because their extent is too great. In many 

 concert-rooms, this difficulty is considerably modified, 

 owing to their being frequently occupied ; whereas 

 churches are rarely warmed more than once in a week, 

 and never attain a genial temperature uutil the daily 

 services are completed, and the requirement has ceased. 



A glass window has a power of cooling the warm air of 

 a church, twenty times greater than that of the walls ; 

 whilst a double glass window reduces this immense waste 

 of heat to about a fifth of that caused by a single one. 



Some years ago, the writer was consulted in reference 

 to this subject, by the trustees of a church in the neigh- 

 bourhood of London. Having placed a number of ther- 

 mometers in different parts of the edifice, whilst the 

 usual heating apparatus was in full operation, the cooling 

 effect of the glass windows was at once evidenced by the 

 lower degree of temperature registered beneath them. 

 The officials, however, could not bo persuaded that the 

 conducting power of the glass was the cause of the ob- 

 noxious draughts, until it was made evident to their 

 senses by filling the building with smoke from brown 

 paper. The currents of air were then easily distin- 

 guished, and the cause was at once seen. The reinnly 

 applied was thick calico blinds, so arranged as to lie close 

 to the glass, and the evil was thereby greatly lessened. 



The employment of steam and hot water for heating 

 purposes, at all times affords a ready means of ventila- 

 tion. In summer-time, considerable difficulty is expe- 

 rienced in obtaining an upward draught for ventilating 

 purposes, because the external air is often at the same, 

 or even of a higher temperature, than that inside the 

 building. In some instances, large furnaces have been 

 erected on the roof. Through these, the air is drawn by 

 the draught of the burning fuel ; and thus an upward 

 current may always be ensured. There is, however, 

 great danger from tire, and also the expense and troublo 

 of carrying up the fuel objections which strongly mili- 

 tate against the adoption of plans of this kind. 



In winter, when hot air is allowed to enter into the 

 lower part of a large room, an ascending current is easily 

 obtained ; and thus, if proper means for its escape are 

 furnished, ventilation may easily be effected. 



Omitting to mention the use of fixed stoves on a level 

 with the floor of any large room, <tc., there are three 

 different means at present adopted for the purpose of 

 warming and ventilation. In each of these, the source 

 of heat is placed beneath the audience, and warm air is 

 admitted from it, and diffused by openings in the floor. 

 Hot air is sometimes produced by allowing external 

 air to pass over iron or brick surfaces enclosing a fur- 

 nace. This plan is objectionable, because of the ex- 

 treme dryness of the air thus produced ; and also on 

 account of smoke and other volatile products frequently 

 escaping and mixing with the current, to the annoyance 

 of all who have to breathe it. 



