24 REPORT — 1856. 



or even three-quarters of an hour. 2. They do not arise from undulatory motion in 

 the whole waters of the harbour. In order to examine this question, Mr. Edgcumbe 

 Chevallier, the storekesjDer in Halifax Dockyard, went to Sambro, ten or twelve miles 

 south of Halifax, and entirely clear of the harbour, and erected upon Power Island 

 a temporary gauge, with which he took the height of the water every five minutes 

 for the whole day. Having laid off the results in a form similar to that employed 

 with the fixed tide-gauge at Halifax, it was found that every irregularity at Halifax 

 was preceded ten or fifteen minutes by a larger irregularity at Sambro. These 

 observations show that the irregular waves do not arise from the peculiar form of 

 the harbour at Halifax. 3. At about sixty miles eastward from Halifax, outside 

 Sable Jsland, the Gulf-stream runs in nearly a north-eastern direction with consider- 

 able velocity; and between Sable Island and the land a counter-current runs nearly 

 in a south-western direction. One of these currents would elevate the surface of the 

 sea near the middle of the currents; and such an elevation of the surface over which 

 the tide-wave is propagated might give rise to undulations similar to those observed. 

 I am informed, however, that the undulations in question are observed on the 

 western side of Nova Scotia, to which any effect of those two currents could not extend. 

 4. Although the tides at Halifax and on the neighbouring coast are small, that 

 part of the ocean is near the indraught of the Bay of Fundy, where the peculiar 

 form of the coast and its position with reference to the great tide-wave of the 

 Atlantic give rise to a local tide of excessive magnitude. Such a tide, espe- 

 cially when reverberated from coast to coast in a comparatively narrow inlet, 

 might not improbably give rise to perceptible undulations in a neighbouring part 

 of the sea. If this be the cause, it might be expected that a similar effect should be 

 noticed where a tide of the like nature takes place. The Bay of Avranches is 

 a locality of this kind, and the island of Jersey appeared to be a place where any 

 undulations of the tide might probably be noticed. The extreme difference between 

 high and low water at St. Helier's is 42 feet, and the difference of height of the 

 mean high and low water is 36 feet. On inquiry, I find that about ten years since 

 a tide-guage was fixed at St. Helier's, but observed only at high water, when 

 irregularities were observed of the same kind as those noticed at Halifax. This seems 

 to give probability to the opinion that the irregularities observed in the tide at 

 Halifax may be connected with the unusual tides in the Bay of Fundy. But 

 whether they arise from this source, or are to be traced to some great reciprocating 

 motion to which the waters of the Atlantic may be subject, the phaenomenon deserves 

 to be studied, as likely to lead to a more extended knowledge of the hydrodynaraical 

 conditions of our globe. 



Working Model of a Machine for polishing Specula for Reflecting Telescopes 

 and Lenses. By Richard Greene, M.D. 



The polishing machine, the model of which I have now the honour of laying before 

 the British Association, scarcely deserves the name of an invention, inasmuch as 

 the public have for some years been in possession of a very beautiful machine, 

 invented by William Lassell, Esq. of Liverpool, and most ably constructed by my 

 very talented friend James Nasmyth, Esq. of Patricroft foundry. It will no doubt 

 occur to most persons acquainted with the very superior specula produced by both 

 these gentlemen with that machine, why trouble the Association with an imitation 

 of that invention ? 



This question is solved by the weighty argument of the three letters £ s. d. 

 The polishing machine of Mr. Lassell is constructed entirely of metal, is quite out 

 of the power of any amateur to construct, requires to be bolted to wall, can scarcely 

 be turned by hand power, weighs at least three or four hundredweight, and from 

 the great care and accuracy required in its construction, costs, I think, £70, while 

 a light portable machine on the principle of this model can, without any difiicultv, 

 be made by any handy amateur with a common foot lathe for less than 70s., and 

 need not weigli 90 pounds. The only machine I ever made on this principle is 

 amply powerful to polish specula of 12 or 14 inches aperture ; its fly-wheel is only 

 2 feet diameter, weighing about 45 lbs., and such a fly-wheel can always be found 

 at the old iron stands for six or eight shillings : all the spindles are common bar iron 



