PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 543 



to get in between the gearing, and soon put it out of order. An 

 attem{?t has been made to propel vessels by a series of buckets 

 attached to an endless chain, by which a number of the buckets 

 are always acting on the water. But there was no advantage in 

 this method, as it is only the first bucket that has any effect; but 

 with the ordinary paddle wheel, it acts on the water from its first 

 entering to its leaving the water. 



Neav Combination of Cranks. 



Dr. Roweil exhibited a model showing how by the addition of 

 a third crank, thus making a triangular connection, the beam of a 

 vertical engine in a sleam ship could be lowered as the vessel be- 

 came lighter by the consumption of coal. 



The exhibition of this iiiodel led to a very interesting discussion 

 regarding the kind of engines best for steamships, and the proper 

 ballastino; of the vessel, in which Dr. Rich and Mr. T. D. Stetson 

 took a prominent part. 



Disinfectants. 



The chairman opened the discussion of this subject with the 

 following paper : 



Disinfectants, in the widest sense of the term, embrace all sub- 

 stances employed to destroy or counteract the effects of all external 

 impurities which are sources of disease. Deodorizers are not 

 necessarily disinfectants. Deodorizers may dissipate a smell, or 

 merely disguise it, by a more powerful and agreeable one. Per- 

 fume is a palliative. Thus musk may mask or drown a disagreea- 

 ble odor, and a scented handkerchief may cover a multitude of 

 noxious emanations. True, disinfectants produce a more important 

 change. They attack and rout the unseen and insideous enemies 

 of health. Contagious diseases, not the result of direct contact, 

 are supposed to be transmitted by a virus floating in the air, which 

 is too small to be seen even with the aid of the most powerful micro- 

 scope, and too subtle to be detected by the most careful chemical 

 analysis. This unknown virus is the offspring of a morliid pro- 

 cess, and is proliably a zymotic organism, possessing vitality. It 

 certainly has the power of increasing, by reproduction or by 

 growth, with fearful rapidity. No remedy has yet been found for 

 the cattle plague still raging in England, and as yet no infallible 

 antidote is known for the cholera that at present infests both the 

 old and the new world. When a contagion, for which there is no 

 specific cure, is raptdly spreading, the only recourse left is to pre- 



