Ut WdooWw^t g^mdrnW Jidb (KIi*. 



MEETING AT WHITCHUECH. 



REMARKS ON ALTITUDES OF HEREFORDSHIRE. 

 WEATHER NOTES, ERRATA, AND MEASUREMENT 

 OF THE RIVER WYE FROM HAY TO THE BRISTOL 

 CHANNEL. 



My remarks have reference chiefly to the question of altitudes of meteoro- 

 logical stations, by which I mean their height above sea level. This is a very 

 important question for all scientific observers, and especially important to those 

 who direct their attention to the rainfall. 



Mr. G. J. Symons writes as follows : — " In all except mountainous dis- 

 tricts the amount of rain collected increases about 2i per cent, per 100 feet of 

 increased elevation ; therefore, it is e%ident that in the greater part of England 

 an error of 50 feet in the height above the sea involves an error in the amount 

 of rain indicated of (30 in. -f 100 x 1'25 = 0'38) about four-tenths of an inch." 

 —Britkh Rain fall for 1867, p. 9. 



This extract sufficiently shows how important it is that every meteorolo- 

 gist or observer should know the height of his station above the sea. In order 

 to determine this important point, we miist either find the nearest bench 

 mark of the Ordnance Sui-vey, and take the levels from that point to our own 

 station, or we must compare the readings of a tested standard barometer with 

 the readings of another placed at a spot where the altitude is known. Of these 

 two methods, tl.e foimer is to be preferred if possible, but the latter, if carried 

 out with skill and care, and repeated several times, will be found to give very 

 correct results. 



Sir Henry James (Director of the Ordnance Survey) tells us that "the 

 Datum Level for Great Britain is the level of mean tide at Liverpool, as deter- 

 mined by our own observations, and it is eight-tenths of an inch above the 

 mean tidal level obtained from the records of the self -registering tide giiage on 

 St. George's Pier, Liverpool." From this datum point levels have been run, 

 to quote Mr. Symons again, " along a network of the principal turnpike roads 

 throughout the countrj', bench marks being cut on millstones, gateposts, 

 churches, and other jiermanent objects along these roads. From these initial 

 lines subsidiary ones and contours have been completed in certain counties, 

 and are in rapid progress in others ; so that in the course of a few years there 



