Royal Astronomical Society. 



information as to the decimal point. But the revolving circle is 

 connected by toothed wheel- vt'ork with two smaller circles, each of 

 which performs one revolution for ten revolutions of the jjrincipal 

 circle, and each of which has upon its circumference ten series of 

 logarithmic numbers. These small circles, then, give us the means 

 of defining the decimal place, in multiplicand, in multiplier, and in 

 product. Thus, the successive figures 1 upon one circumference 

 may stand for -00001, -0001, -001, -01, '1, 1, 10, 100, 1000, 10000. 

 The rotating index of each circle is adjustable ; there are also ad- 

 justable indices on the fixed frame. Suppose, then, we had to mul- 

 tiply 27'42 by 332-6, we should, both in the principal circle and in 

 one of the smaller circles, set the 1 of the moveable circle or index 

 to 27-42 on the fixed circle; but there would be this diflference, 

 that on the principal circle we have no respect to the decimal point, 

 whereas on the smaller circle we should set to the 2742 following 

 the 10, Then for 332'6 we should turn the principal circle from 1 

 to 3326, but we should also turn it two complete revolutions, which 

 would carry the index of the second small circle from 1 to the 3326 

 following 100. Then the figures of the product will be exhibited very 

 accurately on the principal circle, and much less accurately on the 

 first of the small circles, but they would be found in that series of 

 numbers which follows 1000, and the place of the decimal point would 

 thus be exactly defined. 



For the multiplication of three or more numbers, it is necessar)'^ 

 to plant moveable indices after performing the first products ; this 

 process, however, is much less convenient than that with two sliding 

 scales in the sliding rule. 



The Astronomer Royal remarked, that in his opinion this construc- 

 tion is too expensive and too cumbrous to be extensively used. But 

 he wished much to call the attention of members of the Society to 

 the use of the sliding rule, and to the peculiar defect which he had 

 indicated ; and to represent to them the great value of any simple 

 construction, which, while preserving the other advantages of the 

 sliding rule, would eflfectually remove that defect. 



Mr. Drach suggests that a calculating machine, exhibited by Mr. 

 F. Schiereck in 1837 (the construction of which was concealed by 

 the inventor, who wanted 700/. for his secret), might probably be a 

 particular modification of the sliding rule applied to a circular form. 

 He also suggests the addition of other concentric circles to Mr. Bell's 

 scale, in which the trigonometric or other logarithmic numbers might 

 be laid down. 



The Astronomer Royal gave an oral statement of the progress 

 made by Lord Rosse in the mounting of his 6-feet speculum. 



In a lecture delivered on this subject by the Astronomer Royal in 

 November 1848, a detailed account was given of the distortions pro- 

 duced in the speculum by using the telescope at diflPerent inclinations 

 to the horizon, and of the explanation of these distortions suggested 

 by Lord Rosse, and also of the nature of the remedial measures tried 

 by Lord Rosse while the Astronomer Royal was at Parsonstown. It 

 will be sufficient to recall here, that when the edge of the speculum 



