418 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



it has expanded. The brass being softened by the brazing-, has hardly any 

 elasticity, and without the steel, would not go back on a change of tem- 

 perature. Particular attention is given to the brazing, as the least fault in 

 it will render the strips unfit for use. 



Mr. Eead. — As the strips of brass are soldered together, why would not 

 a solid bar and one piece of steel answer the same purpose ? 



Mr. B. Garvey. — The use of thin plates or ribbons arc very essential, in 

 order to make them very sensitive. Solid bars of the same thickness would 

 take a longer time to make any perceptible change. The object is to have 

 the least amount of metal to be acted upon by the heat. We all know the 

 time it takes a large mass to be heated or cooled. There is in this ther- 

 mometer, two small ribbons, which are affected by the slightest change of 

 temperature. 



The Chairman. — The first thermometer was invented by a physician of 

 Padua, named Sanctoria, and is described in a work published by him in 

 162G. It was a rude contrivance for measuring the temperature by means 

 of the contraction and expansion of given quantities of air. The alcohol 

 thermometer, in nearl}^ the same form as now seen in the rooms of the 

 American Institute, was used about the year 1650. This instrument meas- 

 ures the changes in the temperature very clearly, owing to the large scale 

 used, and is of service in the coldest climate, because alcohol has not yet 

 been frozen, but it boils at 1*16, or 36 deg-rces below the boiling point of 

 water, and is therefore almost useless in the laboratory. Reaumur is said to 

 have invented the mercurial thermometer, in 1709 ; but we find that Fahren- 

 heit, in the same year, had subjected mercury in a graduated tube, to the 

 most intense cold of Iceland, in order to place his zero point as low ag 

 possible, and thus pi'cvent the use of the minus sign in measuringv,heat. 

 He tlien placed it in freezing water, and marked that point at 32" ; the 

 tube was then placed in boiling water, and the height of the mercury Avas 

 marked at 212". Artificial cold has been produced far below the freezing 

 point of mercury ; so there seems to be no reason for retaining Fahrenheit's 

 scale, except that its very general use has made it the public standard, 

 Reaumur made a spirit thermometer having the freezing point at 0, and the 

 boiling point at SC^. The Centigrade thermometer has, however, become 

 the favorite among scientists, because the melting point of ice is the zero 

 point, and 100 degrees the boiling point of water ; thus bringing all esti- 

 mates of heat into decimal relations with these well known fixed p(jints. 



The time has already arrived when more accurate and delicate measure- 

 ments are required in scientific investigations than can be made with the 

 mercurial gauge. Numerous trials of solid metallic thermometers have 

 been made, but experience shows that while they are in some respects 

 more convenient to use, they do not Uiark changes of heat with uniform 

 accuracy, owing in most cases to the use of the mechanism requisite to 

 give the index hand a motion perceptible to the eye. The most sensitive 

 metallic thermometer which has come under my own observation, is one 

 constructed by Mr. Russell, a skillful mechanician of Seneca Falls. It con- 

 sists of many zinc tubes standing in a double row on either side of a bar, 

 which is the common fulcrum. The rods are connected at either end with 



