Astronomical Society. 4,Q$ 



currence ; they were probably suggested by Napier's Rods, 

 and are, for the purposes which the inventor had in view, a 

 great improvement upon them. The rods, which are square 

 prisms, contain on each side successively the proposed num- 

 ber in a multiplicand, and its several multiples up to 9 times; 

 and these in the several series of rods are repeated sufficiently 

 often to serve for as extensive multiplications as are ever likely 

 to occur. Thus, if the four faces of one rod contain respec- 

 tively, once, twice, three times, and four times a proposed 

 multiplicand ; another rod will exhibit in like manner 2, 3, 4, 

 and 5 times the same ; a third rod 3, 4, 5, and 6 times the 

 same ; and so on, to nine, and in several cases, more rods. 



The numbers are arranged uniformly upon equal and equi- 

 distant compartments, while, at a small constant distance to 

 the left of each product, stands the number 2, 3, 4, 5, &c. 

 which it represents. Hence, in performing a multiplication, 

 the operator has only to select from the several faces of the 

 rods the distinct products which belong to the respective digits 

 in the multiplier, to place them in due order above each other, 

 to add them up while they so stand, and write down their 

 sum, which is evidently the entire product required, and ob- 

 tained without the labour of multiplying for each separate 

 product, or even of writing those products down. For still 

 greater convenience, the rods may be arranged upon a board 

 with two parallel projections placed aslant at such an angle 

 as of necessity produces the right arrangement. There are 

 blank rods to place in those lines which accord with a cypher 

 in the multiplier ; and the arrangement may easily be carried 

 on from the bottom product upwards, by means of the indi- 

 cating digits. 



A letter was read from Captain Ross, a member of this 

 Society, giving an account of observations made on the Oc- 

 cupation of Jupiter by the Moon on the 5th of April last ; 

 transmitting also an account of observations upon the same 

 occultation, by Mr. Ramage, of Aberdeen, with one of his 

 own 25-feet reflecting telescopes. 



Mr. Ramage observed the immersion. On the approach of 

 Jupiter's satellites to the moon no diminution of their light 

 was perceptible. On coming into contact with the moon's dark 

 limb, they did not disappear instantly, like fixed stars, but 

 formed an indentation or notch in the limb, as if they were 

 imbedded in it, but were at the same time separated from it 

 by a fine line of light. This indentation continued visible 

 until about half their diameters were immersed, when it dis- 

 appeared. All the satellites presented this phenomenon ; but 



Vol. 64. No. 320. Dec. 1824. 3 N the 



