Proceedings of the P olytechkic Association. 1013 



cations tliey afford should lead us to extend, over the entire area 

 occupied by a house, a layer of the same impervious materials which 

 are put into the so-called "damp course" of the walls. Such a 

 superficial stratum can be easily made by a mixture of gravel and 

 gas tar. It would effectually prevent the rising of the water}'^ vapor 

 out of the damp soil, which the " aspiring" effect of a warm house 

 does so much to intensify over the area which it covers. Where the 

 doors and windows fit closely, the draft of chimneys is constantly 

 acting upon the air in the soil covered by the house in the fashion of 

 an imperfectly exhausted receiver, and wliat is thus drawn up must 

 be more or less malarious. Dr. Rolleston refers further to the 

 necessity of removing the subsoil dampness, as a preventive of con- 

 sumption, as shown by the researches of Drs. Bowditch and 

 Buchanan ; and he remarks that there is some little difficulty in 

 reconciling its attainment with the present system of sewerage, but 

 notes, that at Lubeck, the ends of the sewers have been secured by 

 surrounding the ends of the drain pipes with a layer of gravel. 



]\Ir. T. D, Stetson, — Tliis is a very important subject. It does not 

 always happen, however, that a house with a moist foundation is an 

 unkealthy house. I know a house in iSTew England which is built 

 over a spring of clear water, and the health of the inhabitants of that 

 house has always been remarkably good. If I wished to render that 

 house malarious I will tell you how I would do it : I would dam up 

 that spring so as to have stagnant water in the cellar; I would plant 

 trees all round so as to prevent the light of the sun from ever reach- 

 ing the house, and I would build high and tight fences all round so 

 as to cut off all circulation of air. Then I think I would have suc- 

 ceeded in making the house unhealthy. 



Dr. L. Feuehtwanger then read a very interesting paper on breccia 

 and other marbles, illustrating his remarks by some beautiful speci- 

 mens, highly polished. 



The Sceew versus the Paddle Wheei,. 

 Mr. J. K. Fisher read an article from Colburn's Engineering, in 

 which were given numerous instances of the superiority of the screW 

 over the paddle wheel as a means of propelling vessels. Mr. Fisher 

 thought if the commercial question had been left to solve itself, and 

 the paddle wheel steamers had not been aided by government sub- 

 sidies, the screw would have driven them out of use. Attention was 

 called to the advantage possessed by twin screws over single screws. 



