850 Mr Barlow on the Diurnal Variation 



course of this month, however, the varied phenomena which this 

 one exhibited, while every thing besides appeared to partake of the 

 stillness and monotony of this dreary region where it was posited, 

 excited that degree of interest amongst the officers of the expedi- 

 tion which we have endeavoured to describe ; and with the new 

 year commenced a much more extended series of experiments on 

 the daily variation, the variation of intensity, and, in fact, of the 

 whole series of which it is intended to give a general outline in the 

 subsequent pages. 



The detail of the daily variation experiments forms the second of 

 these articles. After describing the needles employed, marked 

 No. 1, and 2., and a third, employed exclusively for determining the 

 changes of intensity ; and also acknowledging the assistance of 

 Lieutenants Sherer, Ross, Messrs Crozier, Richards, and Head, as 

 also that of Mr Hooper for the delineation of a very accurate dia- 

 gram*, offering a graphical exhibition of the several changes ; the au- 

 thors proceed to take a sort of general review of their results, as fol- 

 lows : 



" Soon after the observations were commenced, it was ascertain- 

 ed that, twice in every four and twenty hours, the needles moved 

 past a certain point, which may be denominated the zero, or mean 

 magnetic meridian ; a fact which was first rendered clearly apparent 

 from the accompanying diagrams, already mentioned, by which it 

 appears, that, in every instance except one, both needles every day 

 passed the line in question. On a single day, February 24., the 

 needle No. 2. did not arrive at it during its eastern motion. 



" The means of the times of the needle passing this zero, as de- 

 duced from four months* continued observations, is 6 hours 15 mi- 

 nutes A, M., and 4 hours 37 minutes p. m., the mean time in each 

 month being as follows : 



6 15 4 37 



To avoid the insertion of many useless figures in the tables, the 

 resulting amount of easterly or westerly dejiection on each side of the 

 zero has been computed. 



The maximum westerly variation at Port Bowen, appears from 

 these observations generally to have occurred between the hours of 

 10^ A. M. and V^ p. m., the mean result of 120 days' observations 

 being ll'^ 4.9"^ a. m. The minimum westerly variation, or the 

 greatest deflection of the north end of the needle to the eastward, 

 took place between 8^ p. m. and 2^ a. m., the mean time deduced 

 as above being 10^ V^ p. m. 



* In order to give an idea of this diagram, we have given a sketch of it in Plate 

 v., for six days, viz. from the 20th to the 26th of March, 



