328 On the Building for the Melbourne Telescope. [Mar. 4, 



The behaviour of the large thermometers may thus be referred to their 

 greater strength ; but it also appears that iu thermometers with cylindrical 

 bulbs great strength will not obviate the necessity of a vacuum-correction. 

 — Added February 27th.] 



13. In order to test the accuracy of the preceding results, the closed 

 cases of the thermometers were opened ; hence all instruments were in the 



same condition when the 



receiver 



was 



exhausted. 



The result 



was the 



following : — 















Thermometers. 



A. 



A'. 



B. 



B'. 



C. 



C 



Corrected mean of readings ] 

 before exhaustion J 



► 56*24 



56-03 



56-23 



56-08 



55"i7 



55^3 



Corrected mean of readings ] 



\ 53"65 





54-24 



54'4* 



53-00 



53 - °3 



Corrected mean of readings } 

 after an interval of 26 h 1 5 m J 



1 52-56 



52-27 



52-47 



5 2 "49 



51-87 



51-85 







'■9 



4-0-02 





-0'02 



that is, the difference shown is either inappreciable, or due to accidental 

 causes. 



14. These experiments have sufficiently established the fact that in 

 vacuum-experiments due attention must be given to the causes which in- 

 fluence the thermometers employed in the receiver, and that in delicate 

 experiments an independent determination of the vacuum-correction is 

 indispensable. 



No new explanation of the cause of the permanent fall in a vacuum has 

 suggested itself during the experiments. General Sabine's original expla- 

 nation, that the removal of the atmospheric pressure alters the capacity of 

 the thermometer, is probably the most correct, especially when it is consi- 

 dered that the only objection ever raised against it, that of time reproducing 

 the original state of the instrument, has been proved groundless by these 

 experiments. 



In conclusion I have to thank the President and Council of the Royal 

 Society for defraying the expenses incurred in these experiments. 



IV. ec Account of the Building in progress of erection at Melbourne 

 for the Great Telescope." In a Letter addressed to the Pre- 

 sident of the Royal Society by Mr. R. J. Ellery, of the Obser- 

 vatory, Melbourne. Communicated by the President. Re- 

 ceived February 27, 1869. 



Observatory, Melbourne, Jan. 4, 1860. 



My dear Sir, — The telescope has at length arrived, and we are now 

 very busy getting it erected ; for nothing could be done towards it till the 

 great machine itself came to hand. It will be nearly two months before it 

 can be fairly tried, when a spacious rectangular building and its travelling 

 roof will be completed. 



Mr. Le Sueur arrived nearly two months before the telescope, having 



