Mr. Lassell at Malta. 131 



MR. LASSELL AT MALTA. 



Me. Lassell lias addressed a letter to tlie AstronomiscJie Nach- 

 richten, giving some account of his proceedings at Malta during 

 the term of a three years' residence now drawing to a close. 

 He describes his telescope — a Newtonian reflector — as monnted 

 equatorially, in a manner generally resembling that on which 

 his 9-inch and 2-feet telescopes were mounted, as described in 

 the Memoirs of the Astronomical Society. " The aperture is 

 nearly 4 feet. There are two large specula, respectively of the 

 foci of 441*8 and 448*1 inches. They are about 4i inches 

 thick, and weigh separately about 2700 lbs. The length of the 

 tube is 37 feet, and its diameter 4 feet 3 inches. It is a lattice 

 or skeleton tube, made of flat bars of iron, joined (with spaces 

 between them nearly equal to the breadth of the bars) by 

 flange rings at convenient distances." The object of this con- 

 struction is to avoid chimney currents in the tube. No roof 

 covers the telescope ; but the observer is placed in a tower, 

 one or other of whose stories commands the eye-piece at any 

 elevation required. The stories of the tower are 4| feet 

 square and reached by an internal staircase. The tower itself 

 is carried round by a circular railway. It can also revolve on 

 its own axis, and it has a radial motion to or i from the tele- 

 scope. 



Instead of a driving clock, which Mr. Lassell considered 

 would be inconvenient from the great weight of the apparatus, 

 he has a system of wheel-work terminating in a fly-wheel and 

 winch handle. By turning the latter exactly once in a second, 

 any object is kept in the field, and a peasant can do this by 

 accommodating his movements to the indications of a loud 

 ticking clock. This motion can be stopped, accelerated, or 

 retarded at pleasure, and not being at all laborious, " can be 

 continued for hours without being oppressive." 



" Attached to the regulating clock are two dials, the finger 

 or index of one of them having a retrograde motion and the 

 dial figured accordingly ; while the other is direct. The first 

 of course belongs to the eastern hour angle, which is constantly 

 diminishing — the second to the western. Being set to the 

 present hour angle at the commencement by the observer, if 

 from clouds, or any other cause, the observation is interrupted, 

 the assistant can, by mere inspection of the dial, bring up the 

 telescope to correspond with it by another winch having a 

 quick motion, without the observer having to descend from the 

 tower, or interfere in any way." 



Among the planets, Neptune has received Mr. LasseU's 

 special attention, and he says " the known satellite is so well 



VOL. VII. — NO. II. E 



