9 , 
MAJOE-GEKEEAL SAEIXE Olf THE DECEA^XIAX 
two classes of solar-diurnal variation (viz. in the mean diurnal variation occasioned by 
the disturbances of large amount, and in what ^may be termed the more regular solar- 
dimmal variation), and the non-existence of a similar decennial period in the case of the 
lunar-diurnal variation, that I have been induced to make these results the subject of a 
communication to the Royal Society. 
The observations at Hobarton comprise, so far as I am aware, the most extensive con- 
secutive series of magnetic observations that have hitherto been made. The hourly system 
was adopted there from the first commencement of the Obseiwatoiy. "We owe it to the 
zeal and clear-sightedness of Captain (now Admiral) Sh Jaiies Claek Ross, by whom the 
Hobarton Observatory was established, that this improvement upon the two-homiy 
system proposed by the Royal Society was introduced. Its superiority for many of the 
contemplated objects of the Observatories was speedily recognized, and the example 
followed at the Ordnance Colonial Observatories, by the employment of one additional 
non-commissioned officer at each, thus enabling the number of daily observations to be 
doubled at the small extra expense of about £24 a-year for each obseiwatory. The- 
duties of “ Observer,” which at the Ordnance establishments were perfoiTned by non- 
commissioned officers of the Royal Artillery, devolved at Hobarton upon the officers of 
the Royal Navy who formed ihe personnel of that Observatory: and I gladly avail myself 
of this opportunity of placing on record, that to the steady and mu’emitting zeal of Com- 
mander Joseph Henry Kay dming the whole period of eight years, of Lieutenants Peter 
Scott and Joseph Dayman for the first fom- years, and of Lieutenants Alexander Smith 
and Francis Simpkinson dming the last four years, are primarily due whatever results 
may now or hereafter be derived from the Hobarton observations*. 
The observations of each month, arranged in the same forms as those of the Ordnance 
establishments, were transmitted by the Admiralty to my office at Wooluich, and have 
been printed. For the purpose of this examination they have been treated precisely as 
those of Toronto, as described in the Philosophical Transactions for 1856, Ait. XVI. and 
Art. XXH. The aggregate number of the observations of the Dechnation at Hobarton 
which have been passed through those processes of reduction is 56,202 ; of these, 4207 
were found to differ from the monthly normal at the same horn- by an amount wliich 
equalled or exceeded fom' scale-divisions, or 2'- 84 in arc value, and were accordingly sepa- 
rated from the rest, for the purpose of deducing from them the periodical laws of the 
class of phenomena to which they belong. The monthly normals, derived fi-om the great 
body of the observations after the exclusion of the distmhances of fom- scale-diiisions and 
upwards, have been employed to show the variation in amount in the different years of 
the mean diurnal solar influence, forming what is generally understood as the regulai' 
solar-diurnal variation ; and the same observations, 51,995 in number, rearranged accord- 
ing to the lunar horns to which they respectively most nearly approximate, have supphed 
the mean lunar-dim’nal variation in the different years treated of in tliis commmiication. 
* In mentioning the names of the observers, that of Mr. Jeffeet, for several years assistant to Captain 
Kat, should not he omitted. 
