8 Mr. Pickering’s Eulogy on 
(§ 197), in which the Jerrestrial refraction is noticed, while this 
was neglected by Robertson, Moore, and others, and of course 
their tables are defective. His thirteenth Table contains the Dip 
of the horizon for various heights, calculated also by the rule in 
Vince’s Astronomy (§ 197), in which the ¢errestrial refraction is 
likewise allowed for. In this Table all the numbers differ a little 
from those published by Dr. Maskelyne, who had made a different 
allowance for that refraction.* 
I ought to add here, that Dr. Bowditch was enabled to give the 
greater accuracy to his work by means of a collection of Manu- 
script Journals of his seafaring townsmen, preserved in the valuable 
Museum of the East India Marine Society in Salem. By a regu- 
lation of that Society, which it is believed was proposed by Dr. 
Bowditch himself, each member, when going upon a voyage, is 
furnished with a blank book, uniformly ruled and prepared for the 
purpose of keeping a journal of nautical and other observations 
and remarkable occurrences; on the termination of the voyage 
each journal is deposited in the Museum of the Society; and the 
whole collection of them, now amounting to many volumes, forms 
a repository of innumerable facts, in nautical and geographical 
science, not to be found in any other sources. 
In connexion with this subject I may here add, that he em- 
ployed himself during three successive seasons, 1805, 1806, and 
1807, with two intelligent assistants, in making a thorough hydro- 
graphical survey of the harbours of Salem and three neighbouring 
towns; of which he published a well-known chart, of surpassing 
beauty and accuracy. With such extraordinary precision was this 
laborious work accomplished, that the pilots of the port discovered, 
and were the first to observe to the author, that their established 
* See Note D, at the end. 
