2 3 o THE POPULAR SCIENCE MONTHLY. 



The depth to which water will freeze has never yet been determined ; 

 but measurements of the formation of ice which are to be carefully 

 made at the observing-stations will, no doubt, materially assist in a 

 determination of this important question. 



At Churchill the harbor-ice forms, on an average, about the middle 

 of November, and breaks up about the middle of June, and these two 

 dates may therefore be taken as marking the extreme limits of the 

 season during which that harbor may be used. 



With regard to the time consumed in making the passage through 

 the strait, it is necessary to note that, had the Neptune gone direct 

 from Cape Chudleigh to Churchill, instead of coasting and working 

 across the strait, there would have been no greater delay on account 

 of the ice than forty-eight hours at the most ; but, at the same time, 

 no ordinary iron steamship, built as the modern freight-carrier is, could 

 have got through the heavier ice without incurring serious risk, if not 

 actual disaster. 



There is one matter to which Lieutenant Gordon draws attention 

 that will require the serious consideration of mariners navigating these 

 waters, namely, that in working through the strait, especially at the 

 western end, he found the ordinary compass so sluggish as to be prac- 

 tically useless. The Sir William Thomson card, however, worked 

 admirably when properly compensated. The reason of this difficulty 

 with the ordinary compass is that, from the proximity to the magnetic 

 pole, the horizontal directive force of the earth's magnetism, which 

 alone directly affects the compass-needle, is very small compared with 

 the whole magnetic force, and consequently the effect of induced mag- 

 netism in the iron of the shij) on the compass becomes very large in 

 comparison with the direct action above mentioned, the result being 

 that, in an imperfectly compensated compass, the error due to local 

 attraction is very greatly increased. The means of correcting this 

 error in the Sir William Thomson binnacle are perfect and easily 

 mastered, and the system is such that the compass can, after the first 

 voyage or two, be perfectly compensated by using certain proportions 

 of soft-iron bars and magnets as correctors, the proportion having to be 

 determined by actual observation and experiment on the voyage. All 

 steamshijjs making the voyage through the strait, Lieutenant Gordon 

 therefore concludes, should have one of these compasses as a standard, 

 and the captains should familiarize themselves with the methods of 

 correcting them, and, as opportunity offers, take azimuth observations, 

 both stellar and solar. 



Great caution will have to be observed by all vessels approaching 

 the strait in thick weather, owing to the strong southward current 

 there prevailing, which, during the forty-eight hours the Neptune was 

 lying-to, swept her forty miles out of her course by dead-reckoning, 

 showing that the amount of southerly set exceeds that indicated by 

 the Admiralty directions. Then, again, the tides rise to a consider- 



