T90 CARNEGIE INSTITUTION 



Modern American engineers have reached the conclusion that 

 either in warming or cooling apartments diffusion of the air, unaided 

 by stirring, cannot be relied upon to produce substantial uniformity 

 of temperature. Air of nearly the desired temperature must be 

 forced to circulate through the room at velocities which are sensible, 

 but are not necessarily great enough to constitute deleterious drafts. 

 In my opinion, cold air should be admitted in summer at numerous 

 openings near the ceiling of rooms, while heating should be effected 

 in winter by warm air entering at many openings in or near the 

 floor. Ventilation should not be left to natural draft alone, for 

 this sometimes fails ; it should always be possible to control it by 

 electric fans or other engines. Thermostats should be employed, 

 but they should be of very solid and durable construction, and they 

 should be carefully checked until found entirely satisfactory. 



Suggestion that Vibration of Piers be Damped. 



The subject of stable piers is one of the most vital importance to 

 laboratory construction, yet it has been most imperfectly investigated. 

 There is no question whatever that superficial vibrations of the soil 

 are largely cut off by a trench excavated about a pier, and for this 

 reason the whole new laboratory at Leipzig is inclosed in a trench. 

 On the other hand, the base of a pier under ordinary conditions is 

 its stablest portion, so that the top of a tall pier vibrates far more 

 than its base. It occurred to me that the vibrations of a tall pier 

 might be damped, for example, by filling the trench about it with 

 coarsely ground cork or some similar substance. I seemed to see an 

 illustration of this principle in Wiechert's seismometer, an instru- 

 ment which is, of course, intended to respond to the most minute 

 vibrations. Except for a very essential device, this seismometer, 

 when once agitated, would continue to vibrate for a long time with 

 a period of its own. This would, of course, defeat its purpose. To 

 render it a " dead-beat " instrument, it is damped by air cataracts, 

 and thus records only the tremors communicated to it by the earth. 

 Now, why should a pier not also be damped by air cataracts, cork- 

 packing, or other means ? In Leiden I met what seems a most sur- 

 prising confirmation of this idea. The Cryogenic Laborator)- and the 

 astronomical observatory are built on soil which overlies some 40 feet 

 of soft mud resting on sand and clay. This seems a most unpromis- 

 ing position for stability, yet experience has shown that it is not so. 

 The piers are built on groups of piles driven well down into the 



