On the Barometric Measurements of Heights. 79 



not needed, while the speed and small cost of aneroid work 

 are so advantageous. 



Having taken, on several occasions, the optimistic view in 

 this matter, I felt it desirable to submit some results justif)^- 

 ing this opinion. The instruments with which the results I 

 propose to quote were obtained, are the following : — 



1. A small compensated aneroid supplied by Kilpatrick 

 and Co., about fifteen years ago. It is a good instrument of 

 its kind, and when tested at the Observatory under the air 

 pump, showed great sensitiveness, the hand responding 

 promptly to the smallest change of pressure. At the same 

 time, I do not suppose it is better than many others that 

 have been exposed for sale by Melbourne opticians. 



2. A large open-faced aneroid, not compensated, with a 

 five-inch dial, supplied by the same firm about twenty years 

 ago. This was an exceedingly cheap instrument, but happens 

 to be unusually sensitive, responding to a variation of pres- 

 sure represented by o^oth inch of mercury. This instrument 

 I used many years ago in laying out contour lines on the 

 Geelong waterworks, and found the lines so laid out, when 

 subsequently tested by levelling, to be almost always within 

 three feet of the right level. I should add that I was aided 

 by accurate level marks about fifty feet lower down the 

 slope. 



3. A new Watkin aneroid, supplied to the University by 

 Kilpatrick and Co., jewelled and compensated, and having a 

 scale so open that a movement of the index corresponding 

 ^o Tijoot'h inch of mercury is visible. This instrument is 

 marked No. 161 on the dial. 



4. An aneroid barograph marked Kilpatrick and Co., 

 Melbourne, and purchased last year. This instrument keeps 

 a constant record of the pressure of the atmosphere, and as 

 far as I have tested it has worked satisfactorily. 



The first experiment that I wish to describe was made 

 about twelve years ago. Four readings were taken with 

 instrument No. 1, on the crest of the dam of the Pipehead 

 reservoir, Geelono; Water Works. These readinos were 

 taken at intervals of three or four hours, and were compared 

 with simultaneous readings on the mercurial barogTaph at 

 the Government Observatory, corrections for temperature 

 and for instrumental errors being applied. The true 

 difference of level by levelling was 760 feet, and the 

 distance about forty miles, the intervening country being 

 nearly level and generally devoid of trees. The four 



