Apeil 6, 1900.] 



SCIENCE. 



535 



true state of knowledge can be obtained. 

 Besides the knowledge of having discovered 

 facts and relations which will enter into the 

 structure of a growing science is the great- 

 est source of pleasure that the student can 

 obtain. 



G. A. Miller. 



COEJfELL UNIVEESITY, 



TBE 31ECHANICS OF SLOW MOTIONS. 



The slow continuous motion of a plastic 

 solid (such as clay, wet sand, wax, tallow, 

 lead, etc.), is a phenomenon of considerable 

 interest to elasticians not only because of the 

 natural interest attaching to this remarkable 

 class of solids, but primarily because it is 

 only during the very slow motions of these 

 solids that it is possible to sharply distin- 

 guish them from the class of ultra- viscous 

 liquids. It is possible to conceive of a 'per- 

 fectly plastic solid,' which, as an ideal 

 body, is altogether free from viscosity, just 

 as we may conceive of a theoretical elastic 

 solid or of an ideal perfect fluid. It is not 

 so easy, however, to secure experimental 

 data upon which one may base his theoret- 

 ical investigation of the motions of plastic 

 solids and by which his conclusions may be 

 tested. 



It occurred to me a few years ago that 

 the kinetoscope offered a ready means of se- 

 curing almost any desired magnification of 

 the rate of these slow motions and thus pre- 

 sented to us a method of securing the lines 

 of flow and rates of motion for anj' desired 

 case. The method that I selected for that 

 purpose was as follows : Let the moving 

 body be photographed upon kinetoscope 

 film at stated intervals — every few minutes, 

 or every few hours, as the case may require. 

 After a suflBcient number of these photo- 

 graphs have been obtained, the film may be 

 run through an ordinary projecting kinet- 

 oscope at the usual rate. In this way the 

 motion that has required several weeks for 



its production may be reproduced upon the 

 screen within the limits of a few minutes or 

 seconds. I have magnified in this way the 

 rate of motion about 500,000 fold, but of 

 course there is no major limit to the possi- 

 ble rate of magnification. I made the first 

 application of this method of magnifying 

 slow motions to the motion of growing seed- 

 lings. Several peas and beans were placed 

 in a glass root cage containing wet sand. 

 The photographs were taken by artificial 

 light at fixed intervals day and night for 

 about three weeks. When the film is run 

 through the kinetoscope the entire growth 

 for the period of three weeks is reproduced 

 in a few seconds. I found the motions of 

 two peas, which were placed upon the top 

 of the soil, especially interesting. These 

 peas found it almost impossible to get their 

 roots into the soil. In one case the root 

 came out of the top of the pea and made 

 directly for the moist soil. It found this 

 too hard to penetrate, but the root contin- 

 ued to grow, the result being that the pea 

 was rolled about the root cage in a very 

 grotesque manner, the root curving and 

 writhing much like an angle worm strug- 

 gling to get into the soil. 



The kinetoscope also shows very clearly 

 the different speeds at which the various 

 parts of the plant grow, and the different 

 speeds at which the same part grows at dif- 

 ferent times. The greatest varietj' in the 

 rate of growth exists, as I suppose is well 

 known, and of course the kinetoscope brings 

 out the relative rates of growth in a very 

 truthful and graphic manner. I regret that 

 my first film does not show any consider- 

 able part of the growth of the stems of the 

 plant, as after growing a few centimeters 

 the stems opened the lid of the root cage and 

 passed out of range of the camera. 



The rather startling results of this method 

 as applied to growing plants has caused me 

 to give some further attention to the matter. 

 At the present time I am preparing some 



