406 



THE POPULAR SCIENCE MONTHLY, 



CORBESPONDENCE. 



YIBEATION OF EOCKS. 



Messrs. Editors. 



REFERRING to Dr. Garretson's com- 

 munication in the February number 

 of " The Popular Science Monthly," relating 

 to rock-vibration in the Patapsco Valley, I 

 would state that a like phenomenon has 

 often been manifested at Cuyahoga Falls, 

 Ohio, and has been the subject of much cu- 

 rious speculation on the part of the inhabit- 

 ants of that village. It has been supposed 

 that the vibrations were caused by the water 

 flowing over the river-dams, but the mystery 

 has been, why the effect should be produced 

 at such great and irregular intervals. Some- 

 times the vibrations do not occur with no- 

 ticeable force within intervals of less than 

 one or more years, and yet the quantity of 

 water flowing over the dam increases and 

 diminishes almost continually within its 

 maximum and minimum limits. When the 

 rock-vibrations occur they produce an in- 

 termittent rattling of loose window-sashes 

 and jarring of buildings. The Cuyahoga 

 River, which runs through the village, is 

 about fifty or sixty feet wide at the first 

 dam. The height of the dam maybe twelve 

 feet. The back water extends about two 

 miles, the banks being sloping and of mod- 

 erate height. Below the first dam the river 

 runs through a rapidly descending rocky 

 gorge, there being four or five dams within a 

 distance of about half a mile. W. F. H. 

 Cuyahoga Falls, Ohio, February 19, 1SS2. 



DEFINITIONS OF MATTEE AND 

 FOECE. 

 Messrs. Editors. 



I write to ask whether the following 

 definitions, distinguishing the three states 

 of matter, have ever been given to the pub- 

 lic. I have not found them in any text- 

 book. Also, whether the test given herewith, 

 distinguishing the two kinds of forces, has 

 ever been formally stated in any scientific 

 work. If not, I think it would be well that' 

 they should both appear in " The Popular 

 Science Monthly." I submit them to your 

 consideration : Definitions distinguishing the 

 three states of matter. A solid is matter 

 whose cohesion is greater than gravity upon 

 its particles. A liquid is matter whose 

 gravity is greater than the cohesion of its 

 particles. A gas is matter, the repellent 

 force (or heat) of whose particles is greater 

 than gravity and cohesion combined. Test 

 distinguishing the tivo kinds of force. All 

 forces are divided into two kinds, attractive 

 forces and motive forces, or attractions and 

 motions, and may thus be distinguished : All 

 motive forces can be insulated ; no attract- 

 ive force can be insulated. Had this test 

 been understood in the days of Newton, it 

 might have saved the scientific world im- 

 mense experimental labor. 



Respectfully, 



E. II. Randle. 

 Eiplet, Tennessee, May 2, 1882. 



EDITOR'S TABLE. 



SPENCER'S DESCRIPTIVE SOCIOLOGY. 



THEEE are many who will regret to 

 learn that this great work has 

 been brought to a close. It has not 

 been carried, as far as its projector origi- 

 nally intended, but still we can not say 

 that it has stopped prematurely or re- 

 mains merely as a fragment. On the 

 contrary, it is substantially accom- 

 plished. It wasalarge enterprise, broad- 

 ly conceived by Spencer twenty-five 

 years ago, as a comprehensive basis on 

 which to build the superstructure of so- 

 ciological principles. The undertaking 



involved a carefully digested method of 

 collecting and classifying all the main 

 orders of facts which represent the con- 

 stitution and characteristics of different 

 human societies, in a form suitable for 

 convenient reference and ready com- 

 parison ; and it was on a scale that im- 

 plied the co-operation of several schol- 

 ars working through many years to 

 execute it. It was inevitable that this 

 task should be of gigantic proportions 

 and involve enormous labor, because 

 social generalizations, to have value, 

 must be based upon that which is both 



