86 



Popular Science Monthly 



the operator then presses another 

 button to return the money to the 

 caller, just as in other pay- telephone 

 systems. 



This accessory has a credit fea- 

 ture, however, which is unusual. 

 In case the tenant is out of change, 

 the operator releases a brass check 

 of the size of a nickel from the coin 

 box. The tenant uses this, and 

 when the manager comes around to 

 collect the coins deposited, the 

 tenant redeems these from him. 



The tenant depos- 

 its a coin in a slot 

 just as in a public 

 telephone. This is 

 carried to the coin 

 box when the con- 

 nection is made 



GERMS HELD UP BY 

 JET OF DRINKING CUP 



Changing the Apartment Telephone 

 into a Pay-When-You-Call System 



ANEW telephone device deserves a 

 Carnegie medal for furthering the 

 cause of universal peace between tenants 

 and apartment house managers. It enables 

 the manager to collect at the time of the 

 calling, and protects him and the 

 tenant as well from being over- 

 charged. 



The coin-collecting device works 

 entirely independently of the regu- 

 lar telephone system. Thus, 

 the tenant calls the operator's 

 switchboard in the apartment 

 house lobby and is connected 

 with central just as usual. 

 But before the operator ac- 

 tually connects the tenant with 

 central, she connects the coin- 

 collecting box in the tenant's apart- 

 ment with a recording box on her 

 switchboard prefacing the action 

 with a request for "Five cents, 

 please." The recording box signals 

 her the instant the nickel is placed 

 in the collecting box. If central 

 obtains the person called, the opera- 

 tor then connects him with the 

 tenant, and by pressing a button, 

 deposits the nickel in the coin box. 

 If the person called cannot be found, 



Be Thou Wary of the 

 Bubbling Cup 



APR9FESSOR in a western 

 university has discovered that 

 small organisms lodge in a great 

 many kinds of bubbling-cup drink- 

 ing fountains, and for a curious 

 reason based on an ancient physical 

 principle. 



Twenty-five years ago writers of 

 textbooks on physics had not the 

 wealth of material to draw from 

 that is now available. In carrying out one 

 of their few experiments a rubber-tube-and- 

 spout arrangement was prepared in such a 

 way that it could be attached to an 

 ordinary water faucet and a small jet of 

 water was projected directly upward. In 

 this jet a small ball would be placed — 

 and, curiously enough, would remain in the 

 air, almost stationary, held up by 

 the jet. The jet seemed to clutch 

 the ball and hang onto it instead of 

 throwing it away. The stream 

 would divide under the ball, 

 come up equally on all sides 

 and hold it in place. The 

 sphere might oscillate up and 

 dtown slightly, but otherwise 

 it appeared to be settled per- 

 manently in place. 

 The western 

 professor men- 

 tioned has dis- 

 covered that ba- 

 cilli may oscillate 

 up and down in 

 some kinds of 

 bubbling cups all 

 day long, day after 

 day — in the same 

 way and for the 

 same reason that 

 the sphere did in 

 • the old-time jet. 



The principle 



in accordance 



with which the 



ball is held up 



in the jet 



of water is the 



same as that of the germs 



held in the bubbling fountain 



