PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 621 



right proportioning of the length of oars, and all else, to give to 

 the muscular effort expended the fullest value at this rate, has a 

 by no means insensible effect upon the issue. A view which 

 appears supported by the measured stroke of Oxford against the 

 quicker rate of Cambridge. 



Hachctte, " Traite des Machines," and the late Mr. B. Bevan, 

 C. E., have given also some important experimental results as to 

 animal efforts continued for 1-ong and short times, and Professor 

 Leslie has placed on record some curious observations on this 

 subject. The sedan chairmen of the last century were accustomed 

 to o-o alono; for half an hour, at the rate of four miles an hour, 

 under a burden of 300 lbs., not always equally divided between 

 them, and a case is on record (how trustworthy we cannot say), 

 of half a mile having been done in five minutes and some seconds. 

 For a short distance, sity not more than 100 or 150 yards, the por- 

 ters of Constantinople, or the fachines at Marseilles and other 

 Mediterranean ports, do not refuse a burden of seven or eight 

 hundred weight, carried on the back, Avith which, in a stooping 

 posture, and sometimes aided by a staff in one hand, they travel 

 at the rate of probabl}^ two miles an hour, if not faster. 



THE HYDRODEIK. 



The improved hygdrometer, the invention of Mr. Edson, was 

 exhibited by its manufacturer, Mr. N. M. Lowe, of Boston, Mass., 

 wlio made the followino- statement : 



It has long been known by observing men that air is not healthy, 

 or comfortable, unless it contains a certain amount of moisture — 

 too much or too little being equally unhealthy — and every one 

 who has given much time and thought to the subject of ventilatio;i 

 must be aware how essential it is to know, from some other source 

 than from our own ever-varying feelings, the real state of the air 

 in which we exist, and upon which our life and enjoyment depends. 

 To assist in the solution of this problem, is the object of the hygro- 

 deik. 



In the sitting room, school-room, and sick-room, this instrument 

 •is invaluable, as it shows at once if the air is in an unhealthy state, 

 and points out the remedy. In conservatories, grape-houses, &c., 

 it is very valuable, as it will enable a comparatively inexperienced 

 person to keep the air in a healthy condition for the plants, and 

 thus avoid the pests of mildew and insects. In cotton mills, also, 

 it is necessary to maintain a constant degree of moisture, or the 



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