PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 539 



agent used. The discovery of its pain-alleviating power was made by the 

 late Dr. Wells, of Hartford, Conn. Ether as an anassthetic was intro- 

 duced by Drs. Morton and Jackson, of Boston; chloroform by Dr. Simpson, 

 of Edinburgh. One objection to nitrous oxide, or laughing gas, is, that 

 its first effect is to excite the muscular system. It is said not to be uni- 

 formly efficacious in producing a state of partial insensibility. But there 

 is certainly less danger in taking it into the lungs than the other com- 

 pounds named. I do not think the use of the first three named agents 

 should be discouraged when administered bj'^ skillful hands; the amount 

 of pain and suffering they have prevented, no language can express. 



New Steam Pressure Gauge. 



Mr. Shaw, of the firm of Shaw and Justice, of Philadelphia, exhibited 

 their patent mercurial pressure gauge. Mr. Sliaw said: 



The principle of its operation is the admission of pressure upon pistons 

 of different dimensions giving the mercurial pressure the advantage of 

 area, and thus employing short columns of mercury to balance high 

 pressure. 



It measures the pressure of steam upon the basis that the columns of 

 mercury in the gauge exactly balances the pressure in the boiler without 

 any other opposing medium. 



This instrument is free from the objections urged against gauges made 

 with springs, discs and diaphragms, all of which are liable to crystalization 

 or variation by change of temperature. This gauge being open to atmos- 

 pheric pressure, no imperfect registry can arise, as space for expansion by 

 change of temperature is allowed in the mercury chamber, and no inter- 

 vening medium of compressed air exists as in other mercury gauges. 



The movements of the plunger not being more than 1-100 partof an inch 

 in driving the mercury to the top of the tubes, the friction upon the gum 

 diaphragms is not of any calculable importance. 



Messrs. Rowell, Fisher and Simpson were appointed a committee to exa- 

 mine this guage. 



Electricity and Magnetism. 



The subject for the evening was here taken up. 



Dr D. D. Parmelee. — When I first thought of this subject it appeared to 

 be an easy one to treat of, and one that furnishes very large materials for 

 discussion; but on further reflection I find that, though there are numerous 

 facts connected with it, yet we have by no means as good an idea of it as 

 of heat and light. It is known mostly by its effects, like many other agents 

 treated of in the natural sciences, so it would not be proper or interesting 

 to occupy your time with useless theories; but I will endeavor to confine 

 myself to some prominent facts connected with it. Electricity seems dif- 

 fused over every portion of matter with which we are acquainted, and can 

 be taken from surrounding bodies. It produces both chemical and physi- 

 cal effects. The views of most scientific men are not matured -on this sub- 

 ject, but incline to the theory which the investigations of Faraday tend to 

 sustain. Thermo-electricity is that form of this agent which is developed 

 by the aid of heat. It was discovered by Prof. Seebeck, of Berlin, in 1822. 



