544 



THIJ POPULAR SCIENCE MONTHLY. 



lost ; and Italian astronomy, which for a time languished, is reconquer- 

 ing with marvelous rapidity the rank which the labors of Galileo as- 

 sured to it at the beginning of the seventeenth century. 



-- 



ON DKOPS. 



By a. M. WOPwTHINGTON. 



AMONG the many ways in which electricity is called in to give 

 assistance in various physical investigations, one of the most 

 elegant and interesting is the application of the electric spark to 

 render momentarily visible a body that is rapidly moving or changing 

 its form. The duration of the electric spark is so short probably 

 not more than ^4-5-07; ^^ ^ second that a body, such as a rotating 

 wheel or oscillating rod, moving in a dark room with extreme rapidity, 

 will, if illumined by an electric spark, seem stationary, since the wheel 

 or rod has not time to change its position appreciably during the 

 short instant for which it is visible. If the spark be bright, the im- 

 pression is left on the eye long enough for the attention to be directed 

 to it, and for a clear idea to be formed of what has been seen. 



The writer of this article has recently applied this method to 

 watching the changes of form in drops of various liquids falling verti- 

 cally on a horizontal plate. As usually seen, a drop of water falling 



Fig. 1. 



Fig. 2. 



from a height of ten or twelve inches on a smooth solid substance, 

 such as glass or wood, seems to make an indiscriminate splash. The 

 whole splash takes place so quickly that the eye cannot follow the 

 changes of form ; the impression made by the last part of the splash 

 succeeding that of the first part so quickly as to confuse it. 



A little careful observation, however, shows that the drop passes 

 through very definite symmetrical forms, and that a splash is by no 

 means an irregular, hap-hazard phenomenon. 



Let the reader let fall a few drops of milk, about \ inch in diame- 



