422 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



in the room of the sick, -where it is essential to maintain a uniform tempe- 

 rature. 



It was decided to continue the discussion of philosophical measuring 

 instruments at the next meeting. 



Adjourned. 



'■! 



Americ.\n Institute Polytechnic Association, 

 June nth, 1863. 



Chairman, S. D. Tillman, Esq. ; Secretary, John W. Chambers. 



Measuring Instruments. 



The subject continued from the last meeting was taken up, when Mr. G. 

 Tagliabue exhibited several instruments, among which were two thermo- 

 meters used in the last Arctic expedition of Dr. Hayes. During that voyage 

 they indicated a temperature of TS*^ below zero. Mr. Tagliabue said he 

 was making a spirit thermometer for Captain Hall, for his intended expedi- 

 tion to the Arctic Sea, which would show 90^ below zero. Mr. T. also pre- 

 sented a self-registering thermometer, for green houses, by which the high- 

 est and lowest temperature, during the night or day, could be ascertained, 

 The index having to be reset by a magnet, in possession of the proprietor, 

 only, placed the registering index beyond the control of the person in 

 charge. A mercurial barometer, with an improvement for reading the scale, 

 was next presented by Mr. Tagliabue. 



The Barometer. 



The Chairman. — The barometer is a modern invention. It was brought 

 into use about the middle of the seventeenth century. The investigations, 

 which resulted in the discovery of the pressure of the atmosphere, and the 

 invention of an instrument for measuring this pressure, was commenced in 

 Italy in an attempt to answer the queries of practical mechanics. The 

 pump makers of the city of Florence found that it was impossible to raise 

 water by suction higher tlian about thirty-two feet. In this dilemma they 

 sought the great philosopher of the time, Galileo. He, however, was unable to 

 furnish any satisfactory explanation. The old reason that " Nature ab- 

 horred a vacuum," always given for the rise of water, in the suction pump, 

 was futile, and Galileo's reply to the pump makers was virtually an admis- 

 sion that Nature did not abhor a vacuum above a height of thirty-two feet. 

 This answer was very unsatisfactory to the philosopher himself, and ho 

 made some experiments upon what he called the power of a vacuum. His 

 other duties and liis advanced ago prevented the continuance of his inves- 

 tigations in this direction, but he earnestly entreated his pupil, Torricelli, 

 to pursue the subject. The first, and very important step of the latter, was 

 to ascertain whether the height to which a liquid rose was in proportion to 

 its density. He knew that the liquid metal mercury was about fourteen 

 times heavier than water, and decided to make an experiment with mercury, 

 in a glass tube, so that he could watch the action of the metal. Accord- 

 ingly, he prepared a tube of glass about four feet long and a quarter of an 

 inch in diameter. After hermetically sealing one end, he filled it with mer- 

 cury, and placing his finger upon the open end, he elevated the tube to a 



