1871.] recording Minute Variations of Atmospheric Pressure, 493 



change of pressure, the one rising while the other descends, and so com- 

 bining to produce the desired movement. 



A light but rigid V-shaped bar is laid inverted on the sharp edge of a 

 disk placed on the axis of the pulleys supporting the cylinders, the other end 

 of the bar running upon a light disk as a friction -roller. 



This bar carries a glass capillary siphon pen of very simple form lightly- 

 poised, and having a reservoir of fluid ink sufficient for a month's use ; this 

 traverses the paper on the drum in the usual manner. 



The relative areas of the cylinders and the hydraulic chambers respec- 

 tively determine the scale upon which the curves shall be projected ; the 

 ratio of 10 to 1 which has been adopted giving half an inch rise or fall for 

 one-tenth of an inch difference in the water-level in the two chambers. 



The instrument therefore multiplies by 5, and the difference in the 

 specific gravity of mercury and water again multiplies by 13*59, say 

 13*6 X 5 = 68 ; this is the scale upon which the curves would be projected 

 were it not for the power of self-adjustment given to the instrument, in order 

 to keep it within range. 



By use of an instrument such as described, the writer has at intervals 

 during the last four years accumulated barograms for subsequent examina- 

 tion and discussion, amounting to over 450 days. 



The autographs of different days are as diverse as possible, and sometimes 

 most characteristic ; tracings of a few types are appended. 



It is only within the last few weeks that the writer has been able to com- 

 mence the comparison of his barograms with independent data gathered 

 from a wide area of official observations. 



By the courtesy of the Meteorological Committee of the Royal Society, 

 and the kindness of Mr. Scott, the Director of the Meteorological Office, 

 he has been furnished with all the reports and data at their disposal, which 

 he trusts will enable him thoroughly to discuss the matter. 



Meantime the interesting nature of some of the results, the coinci- 

 dence in point of date between some of the most striking of the micro- 

 barograms, and the existence of storm and gale within a certain radius are 

 not a little remarkable, and are indeed sufficient to induce the writer to lay 

 the matter before the Royal Society in its early stage, rather than await a 

 fuller development under his own hands, in order to insure for it a wider 

 basis than his own individual observations alone could command. 



Personally the writer entertains little doubt that these barograms show 

 the existence, under some circumstances, of the atmospheric storm-waves 

 of which he has been in search, the most marked feature in such case being 

 the rhythmical character and strikingly wave-like form which the minute 

 movements assume. 



It is believed that much information may result from such additional 

 means of research, and the writer offers the instrument in aid of meteoro- 

 logical science. 



The Societyadjournedover the Whitsuntide Recess to Thursday, June 15. 



