PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 431 



Mr. Garvey. — This cephalometer appears to be well adapted for the pur- 

 pose intended. It can be used not only for measuring- the heads of the 

 living, but also of those who have lived centuries ago, to contrast them 

 with those of the present day ; for there are to be had the skulls of those 

 who lived some thousand years ago. A comparison of the head and size of 

 the brains of those who flourished in ancient with those of modern times, 

 would be very interesting. 



Hydrometer. 



Mr. A. R. Callo described Mr. Tagliabue's hydrometer, and showed some 

 experiments with it. lie said that the greatest density of water was 

 between 39 and 40 degrees of tlie Fahrenheit thermometer. From this 

 point the comparison is made of the specific gravities of different liquids, 

 allowance always being made for the temperature of the atmosphere at the 

 time, as the cold of winter condenses the fluid, and increases the specific 

 gravity, while the heat of summer expands the liquid, and causes a dimi. 

 nution of its specific gravity. Alcohol and water unite in every proportion, 

 and the combination is attended witli a decrease of volume, so that a mix- 

 ture of 100 gallons of alcohol and 100 gaHons of water, will make but 190 

 gallons altogether. The density of the mixture increases when the water 

 is in excess of the alcohol ; hence the strength of the spirits may bo 

 estimated by its specific gravity. 



Mr. Garvey. — From the slight cohesion of the particles of fluids, and the 

 ease with which they slide over each other, the iuferenco is that they must 

 be small, smooth and globular, and if they are round there must be spaces 

 between them, in the same manner as there are spaces between balls. lu 

 a like way a certain quantity of sugar ma}' be taken up in water without 

 increasing its bulk, and afterwards salt may be added to it and its bulk re- 

 main the same; by admitting that the particles of water are round, this is easi. 

 ly accounted for. From the mixture of 100 gallons of water with 100 gallons 

 of alcohol, we do not get 200 gallons, as the water seems to fill in the 

 spaces between the alcohol, and we get less than 200 gallons. 



Dr. Rowell. — A soda water fountain that holds 10 gallons, when filled 

 with carbonic acid gas of 10 atmospheres, or 150 pounds pressure, wilj 

 allow 9 gallons of water to be pumped into it, and there will still be but 

 150 pounds pressure. The idea is that the water absorbs the carbonic 

 acid gas. 



Mr. Dibben. — It is well known that carbonic acid gas when at rest, is 

 absorbed, but if shaken up, the pressure will be increased. 



Mr. J. Johnson. — It has been stated that 30 diflerent gases can be com- 

 bined together, and yet the pressure will remain the same 



On motion of Mr. Dibben, the Association adjourned to the 3d of Sep. 

 tember. 



American Institute Polytechnic Association, ) 

 Septeinber 3c?, 1863. \ 



Chairman, S. D. Tillman, Esq.; Secretary, Enos Stevens. 

 After a few remarks from the Chairman, on the influence of fairs, on 

 motion of Mr. J. Bull, the meeting adjourned to attend the fair of the 

 American Institute, opened that evening at the Academy of Music. 



