57 



need assertion ; but if proof be required, we have but to turn to the 

 reports of the survey of the last few years to satisfy the most incre- 

 dulous. Within that time, channels of vast importance to commerce, 

 and before altogether unknown or unused, have been discovered in 

 the harbour of New York and in the Delaware bay; and six unknown 

 and dangerous shoals have been discovered within the last year, lying 

 in the direct track of the commerce between New York and Europe, 

 as well as of the coasting trade between the former place and New 

 England. Of the Delaware bay, until the recent publication of the 

 maps of the Coast Survey, there was no chart upon which reliance 

 could be placed. Some of the most dangerous shoals were placed 

 from three to seven miles in error; the light-house at Bombay Hook, 

 a neighbourhood at one time noted for the number of vessels ground- 

 ing there, was five miles out of place, and the mouth of the bay, be- 

 tween Capes May and Henlopen, was represented from 15 to 18 miles, 

 when the survey shows it to be but eleven and a half. Yet, over this 

 unknown and dangerous ground passed yearly, according to a report 

 made to the government, about the year 1837, by Major Bache, of the 

 Topographical Engineers, an insurable interest created by the coal 

 trade alone, amounting to 822,000,000 per annum, estimating merely 

 the vessels in ballast coming after it, and the value of the vessel and 

 cargo carrying it to the various ports at which it is wanted. Many 

 of these vessels, however, instead of ballast, bring to Philadelphia 

 cargoes of plaster, fish, lumber, salt, dsc, the value of which is, of 

 course, not included in the above estimates; and it is well known that 

 few of these vessels employ a pilot. To such an extent has this coal 

 trade now increased, that while, in 18.36, there cleared from Philadel- 

 phia 3225 vessels, carrying 344,812 tons, the number of clearances 

 in 1846 was 8953, carrying 1,065,228 tons. Along the southern 

 part of our country, the coast is, of course, still less accurately 

 known, since it does not lie in the track of the extensive trade pass- 

 ing over the points which we have alluded to above. These few 

 facts will be sufficient to show the pressing necessity which exists, 

 that a coast so little known, and of so dangerous a character, from 

 its exposure, and the number of its shoals, should be, as soon as pos- 

 sible, accurately and thoroughly explored. 



In order to accomplish a work of such extent with the requisite 

 precision, it is necessary to make available to its purposes all the 

 refinements which mathematical and physical science have added to 

 the art of measurement. The original base lines, which form the 

 starting points of the survey, require to be measured by apparatus of 

 VOL. V. — I 



