ON RAILWAY BAR CORROSION. 101 
loads are light enough not to disintegrate the surface of the rail, and to 
places where the brakes are not applied. On many of the lines of heavy 
traffic in these kingdoms at present the incumbent loads seem from the very 
first to break up the molecular arrangement of the upper flange of the rail, 
and hence induce a gradual increase instead of decrease of abrasion; while 
in places where the brakes are habitually applied, the rails are ground away 
in flakes with great rapidity, those at some of the stations on the Kingstown 
line having one-half the upper flange of the rail cut away in three or four years. 
Through the kindness of Capt. Larcom, R.E., I am enabled to give the 
amount of rain which fell in the basin of Dublin during the period occupied 
in this last experiment. The results are taken from the meteorological re- 
gister kept at the office of the Ordnance Survey, Mountjoy Barrack, Phoenix 
Park, Dublin. The rain-gauges are situated on a plain 181°8 feet above the 
Ordnance datum, or low water of spring-tides, at Dublin Bay lighthouse, and 
have no hills in the immediate vicinity. The annual fall of rain is pretty 
constant at Dublin; and hence these tables may be viewed as sufficiently 
applicable to all the experiments related in this report. 
The average rain, from several years’ registry, is 33°115 inches by Ordnance 
gauge, and 29°616 inches by that of the Royal College of Surgeons in the 
city of Dublin, and at an elevation of 51°72 feet above the Ordnance datum. 


Months. - 1841. 1842. 1843. 1844, 
January ...... 1-767 1:147 1°886 1°726 
February...... 1-210 2°860 1°561 2°517 
Miah its o/+,- 1°635 2°314 1°704 2°058 
1 Sas ae 1-082 | 0-996 | 2-984 | 1:207 
eee oe 2°349 | 3°673 | 4°639 0°295 
eee. oe .-| 2°043 2°256 | 2°887 1-479 
De Cee 2°763 | 3:183 | 2°246 2°039 
August ......| 2°951 1°580 | 2°025 3°634 
September ....| 1°489 3°451 1°235 2°847 
MEDERODEE |. clas) one 4°810 1°734 3°918 2°824 
November ....| 2°781 5°234 2°543 4°992 
December ....| 3°245 1:126 0°414 2°412 
For the year ..| 28°125 | 29°554 | 28-042 | 28-030 
—_— es eee 



The mean barometric pressure for the years 1842 and 1843, corrected and 
reduced to 32° Fahr. at Dublin, was— 
; LbG Wa 0 ler er 29'926 inches, 
LSE ages eae 29°870 inches, 
the cistern of the barometer being 24°5 feet above the Ordnance datum; and 
the above numbers being deduced from 3600 observations. 
For these data I am indebted to Professor Lloyd, who obligingly extracted 
_ them from his results obtained at the Magnetic and Meteorological Observa- 
tory of Trinity College, Dublin. 
The mean pressure at Greenwich, where the barometer is 159 feet above 
the level of the sea, for the years was— 
VBA 5.) 88 Seedy ete ote 29'687 inches, 
UBAO. che sines ate 29°832 inches, 
_ the instruments being strictly comparable. 
The relations to the corrosion of iron, of variable quantities of rain and 
of atmospheric pressure may be referred-to in my Third Report on the 
Corrosion of Iron, Trans. British Association (sects. 286, 305). 
