52 Notices respecting New Books. 



When Mars approaches either of these stars, the observer 

 should, with a micrometer, measure their distance in a direct 

 line ; or take the diffei'ences, in right ascension and declina- 

 tion, between the planet and the star : the place and the cor- 

 rect time of observation being noted down. 



Accurate observations of this kind are of great importance 

 in astronomy: and as nothing tends so much to further such 

 objects as a previous announcement of the phaenomena about 

 to take place, I trust I need not make any apology for drawing 

 the attention of the members of this Society to so interesting 

 a subject. 



The diameter of Mars, on the day of opposition, will be 

 13",91. 



XII. Notices respecting Nexv Books. 



Recently published. 



A Practical Essay on the Strength of Cast-iron and other Me- 

 tals, Sfc. ; the 2nd Edition, Svo. By Thomas Tredgold, 

 Civil Engineer, tyc. 



r j^HIS importantly useful Work, came under our notice too 

 "*■ late in the last Month, to admit our doing little more in 

 p. 451, than announcing its publication: we now therefore 

 resume the subject, with reference to the account we gave of 

 the 1st Edition, in p. 137 of our 60th volume, in order to no- 

 tice, the new matters dispersed through the present Edition, 

 which seems collectively to amount to about 130 pages. 



Instead of the former seven Sectio?is, the work now consists 

 of eleven such, viz. an entire new sixth Section has been in- 

 serted ; the matter of the former sixth Section has, with a great 

 deal that is new, been distributed into four others, which are 

 numbered VII, VIII, IX and X, and the former seventh 

 Section is now the Xlth. Very judiciously, as regards refer- 

 ences, and the quotings of this Work by other Writers 

 (which cannot fail we think of becoming numerous), no altera- 

 tions have been made of the former division of the Work into 

 304 Articles, as numbered in the Margin ; but between these 

 Arts, in various places, the principal new matter has been in- 

 troduced, and numbered and distinguished thus, viz. 6 a , fol- 

 lowing Art. 6; 8 a following Art. 8 : 19 a and 19 b , following 

 Art. 19, &c. And the alphabetical Table of Data, which 

 follows Art. 30 1, might, advantageously for references, have 

 its Articles numbered, in continuation, viz. 305, 306, &c. ; and 

 in a future Edition we hope this will be done. 



In 



