Dkcembee 23, 1921] 



SCIENCE 



625 



the coast of Florida seemed to show tliat flies 

 come down the wind from Cuba (ninety miles 

 distant), and at times from the Marquesas 

 Keys (twenty-four miles distant), and even 

 from Key West, Fla., forty-six miles away. 

 The maximum distance traveled by the house 

 fly in these experiments was 13.14 miles. The 

 tests proved that the injurious forms of fly 

 life were not distributed on any large scale by 

 artificial means, but rather that many of the 

 far-flying species showed marked migratory 

 habits. 



IMPACT ON BRIDGES 



A NEW instrument devised by the Bureau 

 of Public Eoads of the United States De- 

 partment of Agriculture measures with sci- 

 entific precision the effect of every shock and 

 blow delivered by moving vehicles in crossing 

 a bridge. Attached to any part of the bridge 

 structure, this instrument makes a photo- 

 graphic record of the effect of the moving 

 load. The amount of stretching or shorten- 

 ing of the part as a result of the shocks is 

 represented by a fine black line on the photo- 

 graph. No blow or shock can be delivered 

 so quickly that the instrument will not re- 

 cord its effect. It has never before been pos- 

 sible to measure the effect of such blows. En- 

 gineers have long been able to calculate the 

 effect of standing loads very exactly; but be- 

 cause of their inability to measure the effect 

 of quickly delivered blows or impacts, they 

 have never been able to proportion the various 

 parts of a bridge with absolute assurance. 

 It has been necessary to make a liberal al- 

 lowance for this unknown' quantity. In some 

 cases the allowance has not been sufficient and 

 the bridges have collapsed under moving 

 loads. Many bridges still in service are prob- 

 ably too weak to withstand safely the sharp 

 blows of swiftly moving vehicles, though they 

 will safely carry the same vehicles at rest or 

 moving at a slow speed. The familiar warn- 

 ing posted at the portals of a bridge : " Speed 

 limit on this bridge 8 miles per hour," means 

 that the design of the bridge to which it is at- 

 tached is not strong enough to allow for im- 

 pact. In the light of the recent experiments 

 with motor trucks in which it was shovm that 



a swiftly moving motor truck may strike a 

 blow equivalent to seven times its actual 

 weight, it is rather surprising, the department 

 road experts say, that failures have been so 

 few. It is believed this new measuring in- 

 strument will soon do away with uncertainty. 

 The knowledge gained by its use will enable 

 the engineer to design bridges which are sure 

 to hold up under fast-moving vehicles, and to 

 build such bridges without undue waste of 

 material and money. 



THE TORONTO MEETING 



The section of medical sciences of the 

 American Association has arranged the fol- 

 lowing program: 



Vice-presidential Address: " The past and the 

 future of the medical scieuces in the United 

 States ": Professor Joseph Erlanger, professor of 

 physiology, Washington University. 



' ' Hereditary factors in development ' ' : Dr. 

 Charles B. Davenport, director of the Laboratories 

 for Experimental Evolution of the Carnegie In- 

 stitution. 



' ' The metabolism of children in health and dis- 

 ease ": Professor Harold Bailey, Cornell Medical 

 School, N. Y. 



" Newer aspects in dietetics of children ": Dr. 

 Alfred Hess, College of Physicians and Surgeons, 

 New York. 



" Movie exhibition of tonsil-adenoid clinics in 

 operation ": Dr. George W. G-oler, health officer, 

 Rochester, N. Y. 



" The mental hygiene of children" : Dr. C. M. 

 HLncks, associate medical director, Canadian Na 

 tional Committee for Municipal Hygiene, Toronto, 

 Canada. 



Professor E. S. Moere, secretary of the 

 section of geology and geography, writes: 



The section has prepared a very interesting pro- 

 gram for the Toronto meeting and the officers of 

 the section will be glad to hear at once from any 

 of the members who wish to contribute. While 

 the meetings of the other societies affiliated with 

 the association are drawing many of the geologists 

 and mineralogists from this side of the interna- 

 tional boundary to Amherst, quite a number are 

 going to take part in the Toronto meeting and the 

 Canadian geologists are most heartily cooperating 

 in preparation for the meeting. Many of the 

 geologists of the Canadian Geological Survey and 



