1825.] Astronomical Society. H? 



2)ec. 10. — At the meeting of the Society this evening, the 

 publication of the second part of their Memoirs was announced. 

 A paper, drawn up by Dr. Gregory, was read, containing a 

 description of a box of rods, named the lihahdological Abacus, 

 presented to the Society by the family of the late Henry Good- 

 wyn, Esq. of Blackheath. It appears that these rods were 

 invented by Mr. Goodwyn fin- the purpose of faciUtating the 

 multiplication of long numbers of frequent occurrence : 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 number in a multiplicand, and 

 its several multiples up to nine times ; and these in the several 

 series of rods are repeated sufficiently often to serve for as 

 extensive multiplications as are likely to occur. Thus if the 

 four faces of one rod contain respectively, once, twice, three 

 times, and four times a proposed multiplicand ; another rod will 

 exhibit in like manner two, three, four, and five times the same ; 

 a third rod, three, four, five, and six times the same ; and so on 

 to nine; and in several cases, more rods. The numbers are 

 arranged uniformly upon equal and equidistant compartments ; 

 while at a small constant distance to the left of each product 

 stands the number two, three, four, five, &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 obtained 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 indicating 

 digits. ' 



A letter was read from Capt. Tloss, a Member of this Society, 

 iving an account of observations made on the occultation ot 

 upiter by the moon on the 5th of April last ; transmitting also 

 an account of observations upon the same occultation by Mr. 

 Ramage, of Aberdeen, vi'ith one of his own 25 feet reflecting 

 telescopes. Mr. R. observed the immersion. On the approach 

 of Jupiter's satellites to the moon, a diminution of their light 

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

 limb, they did not disaj)pear instantly, like iixed 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 litjht. This indentation continued visible until 



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