LECTURES. 161 



mental illustrations were then given of these rotatory movements. 

 In the external atmosphere the general ventilation of the globe de- 

 pended on such movement. In the smallest space that man could 

 examine they could likewise he traced. A peculiar argand lam{) was 

 then shown, in whicli hundreds of circular rings appeared when the 

 air and gas were permitted to enter in special proportions. They 

 afforded an example of minute rotatory currents indicated by the 

 movement infinitesimally small particles of incandescent carbon. The 

 audience were invited to examine these individually at the end of tlic 

 lecture, as they could not he seen at a distance. Bearing in mind the fact 

 that the living body, unconsciously to the individual, ventilates itself 

 when this operation is not opposed by an air-tight or ill constructed 

 apartment, an aperture for the ingress and egress of air in a proper 

 position^ and of the right dimensions, is the great desideratum. 

 While a window serves this purpose, and a porous curtain diffuses 

 the entering and out going air, it has taken a long time to carry con- 

 viction of the importance of additional resources in the comparatively 

 air-tight structures of modern times, cliarged with products of com- 

 bustion from gas and respiration, as well as other varying impurities. 

 But when it is recollected that a thousand different circumstances- 

 arising from the peculiar position, form, structure, arrangement, fur- 

 niture, and occupation of rooms, as well as their aspect in relation to 

 the sun, prevailing winds, local influences acting on the air, the. 

 position of doors and windows, constitutional peculiarities, and many 

 other details that might be enumerated, in addition to the changes of' 

 the season, the time of day or night, and the number of persons pre- 

 sent, all contribute to modify the effect required, it will be obvious 

 that the window alone is not sufficient for every ordinary apartment.. 

 The great desiderata, in addition to the window, at least in rooms 

 subject to a great variety of occupation, are the following : 



1. A special flue, from the highest portion of the room, for the dis- 

 charge of vitiated air. 



2. A special aperture for the ingress of a warmer or colder atmo- 

 sphere, when the external temperature, dust, noise, or any other cause, 

 renders a supply by the windows objectionable. 



3. The means of extending the diffusion of the entering air so that 

 it shall not impinge offensively on any individual. 



4. The means of applying a force or power to the ventilating flue, 

 (heat is the most available for all ordinary purposes,) which shall in- 

 crease the discharge to any required extent, and cause fresh air to 

 enter by any channel provided for this purpose. 



5. The exclusion of all vitiated air from the basement of the build- 

 ing, or any other source, either by the action of a ventilating flue or 

 other equivalent measures. 



These objects can, in general, be attained with facility and economy 

 in building a new structure, without interfering with the usual de- 

 tails of construction to any objectionable extent. It formis a most 

 important addition when the passages and staircases can be converted 

 into means for the general supply and discharge of vitiated air, warm- 

 ing the air by an apparatus placed there at the lowest available level ^ 

 and introducing a large internal window above every door communi- 



11s 



