186 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



it would be impossible to draw conclusions as to the effects which 

 such tremendous compression would have, influencing the character 

 of the geologic strata with which we are familiar. This point of 

 view is full}- recognized by geophysicists, and similar experiments 

 at very high pressures are being carried on at the geopl^-sical 

 laboratory of the Carnegie Institution at Washington, where the 

 effects of high pressures and high temperatures on terrestrial ma- 

 terials are principal objects of study. 



HIGH PRESSURES AND FIVE KINDS OF ICE. 1 



The experiments which I am about to describe are experiments 

 in the field of very high pressures, which is a practically new field. 

 Under conditions of high pressure many of the ordinary properties 

 of matter are changed ; and the bursting strength of vessels in which 

 such pressures are produced is found to bear no relation to their 

 strength under ordinary conditions. In conducting the following 

 investigations on the effect of very high pressures on water it was 

 found necessary to make many preliminary experiments on the 

 strength of the containing vessels before accurate measurements of 

 pressure could be made. In the course of this preliminary work 

 many interesting facts concerning the behavior of materials under 

 high pressure were disclosed. In this paper will be given, firstly, 

 some of the results of the preliminary experiments on the strength 

 of the containers, and then a description of the experiments made 

 to ascertain the effect of high pressures on water. The paper will 

 be, in large part, a record of my own experimental work. 



By way of introduction it is perhaps desirable to give some idea 

 of the magnitude of the pressures involved. The highest pressures 

 which are ordinarily familiar to us are probably those of modern 

 high-power artillery ; the average firing pressure exerted in many of 

 our large guns is about 2,000 atmospheres, or 30,000 pounds per 

 square inch. The highest pressures reached in the experiments 

 which I am about to describe are 10 times this amount; that is, 

 20,000 atmospheres, or 300,000 pounds per square inch. The pressure 

 exerted at the bottom of the ocean at, say, a depth of 6 miles is about 

 1,000 atmospheres; a pressure of 20,000 atmospheres would, therefore, 

 be exerted at the bottom of an ocean 120 miles deep. If the average 

 density of the rocks of the earth's crust is taken as 2.5, 20,000 

 atmospheres is the pressure which prevails at a depth of 50 miles 

 below the surface of the earth. 



It should be borne in mind that in all the experiments made the 

 pressures were produced in a liquid, which must be held in a con- 

 tainer. It is a comparatively simple matter to produce pressures 



1 By I\ W. Bridgman, Ph. P., Jefferson Physical Laboratory, Harvard Pniversity. 

 Abstracted from Journal of the Franklin Institute, March, 1014. 



