HIDDEN PERILS OF THE DEEP 



829 



taken into account in planning what 

 should be shown on the chart in the first 

 place so as to bring it within the range 

 of practicable revision. 



Certain features are corrected at once 

 on the charts as soon as the information 

 is received, such as dangers reported and 

 changes in lights and buoys. Where 

 harbor works are in progress the periodic 

 surveys made by the engineers in charge 

 furnish data which are applied promptly 

 to the charts. Reported dangers in chan- 

 nels and bars are investigated by special 

 surveys and the information is put on the 

 charts. Examinations are made from 

 time to time for the revision of the fea- 

 tures along the coast line. Complete re- 

 surveys have been made, at long intervals, 

 of some important portions of the coast 

 where there has been evidence of change, 

 and these, when they become available, 

 are applied to the charts. All parts of 

 the coast where the exposed portions are 

 not of very permanent material will re- 

 quire resurveys at intervals, depending 

 on their importance and the rate of 

 change. 



Notwithstanding the great progress 

 made in hydrographic surveys, a consid- 

 erable number of rocks and shoals 

 dangerous to navigation and not previ- 

 ously shown on the charts are reported, 

 averaging nearly 400 each year for the 

 last six years, according to the British 

 reports. Of the 367 reported in 1906, 11 

 were discovered by vessels striking them. 



DOUBTFUL OBJECTS ON CHARTS 



In addition to the problem of perfect- 

 ing the charts as respects omissions in 

 earlier surveys and correcting them to 

 show changes which have actually taken 

 place, there is an important task of im- 

 provement necessitated by the investiga- 

 tion of doubtful objects which have got- 

 ten on the charts and which may have no 

 existence. The uncertainties in many of 

 the earlier positions may be judged by 

 the fact that as late as 171 3 the British 

 "commissioners for the discovery of 

 longitude at sea" offered a reward of ten 

 thousand pounds for the discovery of a 

 method of determining the longitude 



within 60 miles. Compensated time- 

 pieces, which have been so important a 

 factor in improving navigation, were not 

 invented until about 1761. 



On the earlier charts and on those of 

 more remote regions at the present day 

 much work has been sketched rather 

 than surveyed. Even in the better sur- 

 veyed portions reports come in as to 

 dangers or other matters not shown, and 

 if of importance and the report appears 

 to be reliable, these are sometimes at once 

 put on the chart pending further inves- 

 tigation, or in other cases an examina- 

 tion is first made. 



Shoals, rocks, and even islands have 

 in numerous instances been put on the 

 charts from the reports of passing ves- 

 sels, without systematic surveys. Many 

 of these no one has been able to find 

 again, and after repeated searches some 

 of them have been removed. The same 

 island or danger has sometimes been 

 charted in two or more different posi- 

 tions as reported at various times. The 

 treatment of such cases is one of the 

 serious and interesting problems of the 

 chart-maker. It is generally less harm- 

 ful to show a danger which does not ex- 

 ist than to omit one which does exist. 

 On the other hand, a non-existing danger 

 shown on a chart may be the cause of 

 actual expense and loss of time in com- 

 pelling a vessel needlessly to go out of 

 its course. 



It is surprising to note with what lack 

 of care and of sufficient evidence reports 

 of dangers at sea have sometimes been 

 made, and how incomplete are many of 

 the reports even when the existence of 

 the danger is beyond question. It is 

 unfortunately true that some of these 

 reports are the result of effort to escape 

 blame for accident by throwing the fault 

 on the chart. Many such reports also 

 result from various illusory appearances. 



HOW FALSE REPORTS ARE STARTED 



A large tree covered with weeds, an 

 overturned iceberg strewn with earth and 

 stones, a floating ice-pan covered with 

 earth, the swollen carcass of a dead 

 whale, a whale with clinging barnacles 



