[dawson] review of TECHNICAL WORK 45 



brous and difficult to hold at anchor. These investigations were 

 resumed from 1903 to 1908 and again in 1911 and 1912. A better 

 type of vessel was then employed, but it was still too light for the open 

 and exposed situations under examination. The results of these 

 investigations are given in the publications mentioned further on. 



On the Pacific coast, the currents of interest to shipping occur 

 in the passes between islands. They are so swift that it would be 

 impracticable to anchor a vessel in them, and they have therefore to 

 be observed from shore. In most cases, navigation is not possible 

 during the strong run of flood and ebb, but only near slack water at 

 the turn of the tide. It is therefore the time of slack water that needs 

 to be determined. In addition to its service to general navigation, 

 this information is specially valuable to the powerful tugs employed 

 in towing coal and lumber. By knowing the time of slack water, they 

 can arrange their trips to arrive at a pass at the necessary moment; 

 thus saving a large amount of expense in fuel and lost time. In the 

 comparatively sheltered waters of the Pacific coast, a great deal of 

 traffic is thus carried on by towing. 



In dealing with these passes on the Pacific coast, the chief diffi- 

 culty is to arrive at methods of calculation by which tables of slack 

 water can be prepared. With perseverance, and fresh light from similar 

 investigations in Eastern Canada, satisfactory methods are being 

 used for calculation purposes, with gradual improvement in accuracy. 



Tides. — The general plan on which this branch of the work has 

 been conducted, is to establish reference stations in the various 

 regions, corresponding with the type of tide met with. It is not 

 always an important harbour that is most suitable for a reference 

 station, as some solitary island or isolated lighthouse may be found to 

 dominate a large and important region. On the Pacific coast for 

 example, the leading harbours are almost useless for reference pur- 

 poses, because of their special situations. 



For these reference stations, tide tables are published, which are 

 based on observations obtained at them. The various ports and har- 

 bours on the coast are brought into relation with them by simul- 

 taneous observations obtained by tide gauges which are maintained 

 during the summer season only. 



The reference stations when equipped, can be kept in operation 

 continuously, both summer and winter, which is essential for the 

 modern method of reduction by harmonic analysis. The limits of 

 the region which can be referred to each station are gradually ascer- 

 tained. In some cases, stations which were tried, proved unneces- 

 sary; as the region they were intended to cover could be referred to 

 another station. It is highly desirable to reduce the number of these 



