1890.] The Modern Weather Bureau. 29 



fellow-citizen, Mr. A. Gr. Howard. It has been a high privilege to 

 me to enjoy the study of the instructive series of maps compiled by 

 Mr. Howard for the five years past. I show you now the volumes 

 that he has kindly lent me, and can assure you I hope to have these 

 published in America as an important contribution to meteorology, and 

 one by which we in the northern hemisphere may profit almost as 

 much as yourselves. Mr. Howard has rightly appreciated the recent 

 advances in meteorology, and in this special series of twenty large maps 

 he has located the position of the oval or wedge shaped area of low 

 pressure towards which blew the heavy winds that formed your severe 

 , storm of July 22nd, 1889. On this final chart I have drawn what 

 seems to me likely to have been the course of the centre of this low 

 area. Mr. Howard has prudently avoided locating any such hypo- 

 thetical centre, but I myself should not hesitate to say that the winds 

 can be properly described as coursing toward and around a long oval 

 depression. We have in the States observed many such long ovals, 

 sometimes like troughs, but which eventually close up to nearly 

 circular storm centres. 



I may here caution you against a very common error, namely, that 

 low barometer makes the wind. The fact is just the reverse and the true 

 process is as follows : When air becomes buoyant and rises, there may 

 be a slight barometric depression, but this is usually so slight as to be 

 entirely unmeasurable. Air is so mobile that an imperceptible linear 

 gradient sets it in motion, but once in motion the rotation of the earth 

 causes it to deflect a little, and immediately there is set up a vortex 

 motion ; now in all such vortex motions centrifugal force causes the 

 flowing air to press outward and there is a corresponding diminution 

 of elastic air pressure as we go towards the centre— in a storm of 

 small dimensions it is the rate of this diminution that the barometer 

 measures and that we call the gradient while in larger storms the 

 rotation of the earth introduces a further cause for the fall of the 

 barometer — such for instance as we see in the equatorial belt of low 

 pressure and in the arctic and antarctic areas of low barometer. 

 ' Thus in general the observed low pressures and the high pressure are 

 the results of the" movements of the air, while those movements are 

 themselves the results of barometric gradients that are almost in- 

 appreciable and have never yet been observed by meteorologists. 



A single experiment will illustrate my meaning. Let the water in a 

 basin become very still and then carefully open a small hole at the 

 centre. So long as the water flows in straight lines towards, down 

 and out of the aperture, you will see no appreciable dimple at 

 the centre of its upper surface, but so soon as the slightest 

 whirling begins, the dimple appears and very soon becomes a 

 .funnel-shaped hole down to the bottom. This funnel is directly due to 



