390 



REPORT 1869. 



5-8 per cent., the largest quantity being recorded by those gauges which were 

 most easily managed, viz. those 5, 6, and 8 inches in diameter. 



(3) That at Strathfield Turgis the agreement has been still closer, all but 

 the 1 inch and the 24 inch agreeing within 1-5 per cent. 



This last result might partly have been anticipated from two causes, — 

 (a) Colonel Ward's health appears to have compelled him frequently to em- 

 ploy a substitute, and (6) Mr. Grithth commenced with the preliminary dif- 

 ficiilties removed, and information as to possible sources of inaccuracy which 

 previous experimentalists had had to discover by continuous observation. 



Considering the absence of auy trustworthy published observations upon 

 the subject until those under notice were commenced, the lengthy articles 

 published upon it in some of the scientific journals, and the almost universal 

 ignorance upon it which recently prevailed, it is by no means an unimportant 

 matter to have brought to a definite issue. Moreover, considering the various 

 sizes of the gauges used simultaneously in different parts of the country, it 

 is especially satisfactory to find that, instead of ha\ing, as was anticipated, a 

 correction to apply to the observed values, when measured by a gauge of any 

 but a standard size, to convert them into the equivalent indications of that 

 standard size, no such correction is necessary ; for all the most usual sizes, 

 5, 6, 8, and 12 inches diameter, agree within 1| per cent. 



It seems probable that the smaU quantity registered by the 1-inch gauge 

 is solely due to the great difficulty of emptjdng the last drop — by no means 

 an unimportant matter with so diminutive a gauge, for a single grain weight 

 of water corresponds to 0-008 inch, or nearly one ton of water per acre. 

 The excess collected by the gauge 24 inches in diameter is probably ex- 

 plained by the influence of the large mass of metal of which it is composed ; 

 for after nights of heavy dew it generally contains more than any other, and 

 this would naturally result from its greater radiating-power. 



Some slight alterations were made at Strathfield Tur- 

 gis, on January 1, 1869; and with their conclusion on 

 January 1, 1870, the investigation there of the question 

 of the influence of magnitude will probably be termi- 

 nated. 



The results of the examination of rain-gauges during 

 the year are given in exactly the same form as in the 

 last Eeport, and we are not aware that they call for any 

 comment beyond referring, for explanation, to our Report 

 for 1867, p. 466, and the plate there given. Gauge 

 No. 278 being unlike any of those previously engraved, 

 we add the annexed sketch, fig. 2. A is a funnel 4 inches 

 in diameter, B a divided glass tube into which the rain 

 passes. F a stout post, the upper part of which is hol- 

 lowed out at C, half the outer portion, D, being hinged 

 to afford access to the glass ; E is a pad to keep B close 

 up to A. 



It wiU be noticed that the errors of some of the 

 larger float gauges are not given in detail, the testing 

 apparatus not being adapted to them. 



It has been the practice of the Committee in their 

 various Beports to adopt, for convenience of comparison, 

 a decennial grouping of returns, such as 1840-49, 

 1850-59, &c. We are now on the eve of completing 

 one of these decennial periods, and it behoves us there- 



