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VI. On the Tides at Malta. 
By Sir G. B. Airy, K.C.B., F.R.S., Astronomer Royal. 
Received July 14, — Read December 6, 1877. 
Section I. — Introduction. 
Admiral Sir Astley Cooper Key, K.C.B., late Superintendent of the Royal Naval 
College at Greenwich, and formerly Naval Commander of Malta, before leaving this 
country for a foreign station, placed in my hands the original record of tidal 
observations made by a self- registering tide-gauge at La Valetta, extending through 
one entire lunation and through parts of others. On the location and construction 
and use of the instrument I have received from Sir Cooper Key the following 
notes : — 
“ The place of the tide-gauge was about 40 or 50 yards from the entrance of the 
Somerset Dock (which is in the French Creek, so called by us), on the western side or 
left hand when entering the dock. A channel about a yard wide, and 8 or 1 0 yards 
long, led to a deep recess in which the gauge was placed. No ripple was felt from 
the effect either of wind or of ships moving in the neighbourhood. 
“ The float was a copper vessel, nearly spherical, about 8 inches in diameter ; a 
vertical rod attached to it passed freely through a guide, and was hinged to the end 
of a horizontal lever, of which the arms were so proportioned that each space marked 
on the tabular form between the horizontal lines [one-fourth of an inch. — G.B.A.] 
corresponded accurately to an inch rise or fall of the float. Care was taken to ensure 
that the reading on the horizontal-zero line always corresponded to a definite height 
of water. [I remark here that the base-line or zero of horizontal measures is printed 
on the sheets, and that there is no other base-line given by a pencil attached to the 
fixed part of the instrument frame ; I shall refer to this circumstance hereafter. — 
G.B.A.] I can depend on the accurate movement of the float. I have often watched 
the instrument. 
“ The cylinder on which the paper was wrapped revolved once in 24 hours [the 
corresponding length of paper is 20 inches. — G.B.A.], and was adjusted every morning 
when the paper was removed. The accuracy of the movement was however dependent 
on clockwork. The distance between the vertical lines on the sheets was intended to 
represent solar hours. The time was not taken with accuracy, but is intended to 
represent mean solar time at Valetta. The hours given between the lines, such as 
8 a.m., &c., merely indicate that the register of the height of the water midway 
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