Withy. — On Sanitation and Ventilation. 477 



opening into the space a wind blowing directly upon it will 

 produce a strong rush of air up the tube, and very likely a 

 draught in the room, whilst an opposite wind might sometimes 

 check the proper action of gravity. The principle of the action 

 of the Tobin tube is that of a fountain. It provides an 

 entrance for heavy air into a reservoir of light air. The tube, 

 being placed vertically, directs the air, which enters with a 

 slight force, straight upwards, until its greater weight prevails 

 and brings it gently downwards over the room in the form of 

 the spray from a fountain. It descends so gently as not to 

 cause a draught in the room. Plate XLVIIL, fig. 8, will ex- 

 plain the general arrangement of one of these tubes. 



It now remains to consider the measure of the various 

 appliances for removing the warm air and supplying cool. It 

 is not easy to lay down rules which are of general application ; 

 but I think it may be safely stated that, where ventilation 

 fails, it is more often owing to the apertures being too small 

 than too large. All that has to be guarded against is the 

 production of draughts and the too rapid lowering of the tem- 

 perature by admitting the air too fast. This can be readily 

 prevented by closing some of the openings. The provision 

 must depend upon the number of persons likely to occupy a 

 room at one time ; upon the consecutive number of hours that 

 it may be used without an opportunity being afforded for a 

 thorough blow-through ; upon the amount of gas consumed ; 

 and in some cases upon the position of the room in relation to 

 its surroundings. Some writers give rules which it may be 

 useful to apply ; but it is beyond the scope of a short paper 

 and beyond the range of my experience to attempt to criticize 

 these or to suggest others. It may, however, afford a basis for 

 discussion if I give a few particulars of appliances which I 

 have recently had fitted up in a new house. I will only give 

 these for the dining-room, which will also be largely used as a 

 general sitting-room by eight to twelve persons. This room 

 measures 20ft. by 16ft., and is 12ft. high. It will probably be 

 fairly illuminated with four gas-burners, and will rarely have 

 six lighted. It has a fireplace, two windows, one door from a 

 passage, and two from adjoining rooms. "Within the marble 

 fender there are openings through the floor into the joist-space 

 equal to 54 square inches in area; but this is reduced con- 

 siderably by the perforated-copper gratings. On the outer 

 wall a 12in. by 6in. grating is placed over the opening into the 

 joist-space. There are two Tobin tubes, measuring lOin. by 

 2-|in. clear inside, with a fine- wire grating at the top, making 

 an inlet of about 50 square inches. They communicate with a 

 joist-space extending right through the house, with a grating 

 on the outer wall at each end, 12in. by 6in. The lower sashes 

 of both windows are fitted so that they can be raised 2|-in., 



