On the Compressibility of Water. 347 



The answer is obvious. Let every man furnish his barn, 

 us well as his house, with a lightning rod. In the case of 

 such low buildings, a rod, which, without a curvature, may 

 pass up at one end, would cause but a trifling expense, and, it 

 is believed, would, in most cases, prove a perfect security. 

 When the barn is very long, it may be better to let the rod 

 pass over the middle of the roof, or else to have two rods — 

 one at -each end of the building. 



Art. XVI. — On the Compressibility of Water; by Jacob 

 Perkins, Esq. — from the Philosophical Transactions of 

 London; read before the Royal Society, June 29, 1820, 

 and forwarded to the editor of this Journal, by the author. 



(With Notes, by a Correspondent.) 



Having believed, for many years, that water was an elas- 

 tic fluid, I was induced to make some experiments, to ascer- 

 tain the fact. («) This was done by constructing an instru- 



(a) Although the experiments detailed in this paper present the subject of 

 the compressibility of water in several new and interesting points of view, 

 they cannot be regarded as the first by which this property has been ascer- 

 tained to belong to liquids. So early as the year 1764, a series of experiments 

 was instituted by Mr. Canton, (Phil. Trans, Vols. 11 and 12, Hutton's 

 Abridgement,) from which it decidedly appears, that not only water, but 

 liquids in generaf, sensibly expand by removing the pressure of the atmos- 

 phere, and contract under additional pressure. The method of Mr. Canton, 

 for moderate differences of pressure, is susceptible of a high degree of accu- 

 racy, and seems to have been conducted with every necessary precaution. 

 He found that, in the medium state of the thermometer and barometer, water 

 expands one part in 21740 by the removal of the pressure of the air, and 

 undergoes an equal diminution of bulk by subjecting it to the pressure of an 

 additional atmosphere in a condenser. Similar results were obtained, from 

 a series of experiments, directed to the same object, by M. Mongez, in France. 

 Yet most of the continental writers on physics seem unacquainted with these 

 results, and still appeal to the vague experiment of the Florentine academy 

 for the proof that water is incompressible. Deluc found that, on breaking 

 o.ff the sealed end of the tube of a water or oil thermometer, and admitting 

 the pressure of the air upon the column of the fluid, it instantly sunk. But, 

 instead of ascribing it to the compressibility of the fluid, he resorts for an 

 explanation to the hypothesis, that liquids, however carefully purified, still 

 contain a portion of air, which, although chemically combined with the fluid, 

 retains some part of its elastic force, and thus yields to an increase of press- 

 ure. It is somewhat singular, that this conclusion should be quoted with 

 approbation by Biot, in his late elaborate treatise, (1. 1 95.) without express- 

 ing any suspicion that the phenomena may arise from the compressibility of 

 the liquid. That most of the air which ordinarily exists in water tends, on 

 removing the external pressure, to assume the gaseous form, and to rise in 

 bubbles, is well known from experiment; but so long as no more air is 



