Contributions to Scientific Bibliography. 219 



the intensity of the light of* very small stars. The density of 

 these masses, as I have computed, must he less than the one 

 ten-millionth part of that of the mercurial atmosphere in the 

 Torricellian vacuum, to give such a light as we observe, — a 

 tenuity we can scarcely form a conception of. 



Smedley Hall, August 3, 1831. 



Art. V. — Contributions to Scientific Bibliography. By a Cor- 

 respondent. Communicated by the Author. 



The scarcity of a book, which has nothing else to recommend 

 it, is a fact which is hardly worth knowing ; but when the work 

 has any real value, either from intrinsic merit, or from forming a 

 link in the history of science, its scarceness then becomes an 

 object of importance. It is constantly found that errors are 

 perpetuated by writers who satisfy themselves by copying what 

 they find at second hand, and these errors can never be cor- 

 rected without reference to original authorities. It is useful, 

 therefore, to know not only what books are scarce, but also 

 (when it is possible) where they are to be found. It must 

 often occur to those who have access to large libraries, that 

 they meet with works which they had never before heard of; 

 and the books so discovered will sometimes contain matter 

 which had been looked for in vain. Neither is it to be attri- 

 buted to a mere selfish anxiety for accumulation, when any 

 one employs himself in collecting with this view. Much is 

 learned from what is in our own possession, and even in the 

 search for it ; and every one who has indulged himself in col- 

 lecting books, must have often found advantage from what, at 

 the time of the purchase, he did not foresee that he should de- 

 rive any particular use. This of course supposes that he has 

 collected with some discrimination ; and if in that case he should 

 sometimes he induced to give a higher price than he otherwise 

 would for a book in consequence of its scarcity, he is not on 

 that account alone to he blamed. There are other individuals 

 also to whom some anecdotes on this suhject may not be un- 

 interesting ; and the following remarks may hereafter he sue- 



