Feb. i8, i875' 



NATURE 



309 



a reed, which could be kept in continuous vibration by a 

 stream of air. Musically, owing to Mr. Hamilton's 

 immense enthusiasm and perseverance, the result ap- 

 pears to be a success, but is, I think, acoustically consi- 

 dered, something very different from what was originally 

 intended. I believe that the instrument ought to be 

 regarded rather as a modified reed instrument than as a 

 mclified string instrument. 



Let us consider the matter more closely. The sti-ing 

 and reed together form a system capable of vibrating in a 

 number,theoreticallyinfinitc, of independent fundamental* 

 modes, whose periods are calculated by Mr. Bosanquet. 

 The corresponding serits of tones could only by accident 

 belong to a harmonic scale, and certainly cannot coexist 

 in the normal working of Mr. Hamilton's instrument, one 

 of whose characteristics is great sweetness and smooth- 

 ness of sound. I conceive that the vibration of the 

 system is rigorously or approximately simple harmonic, 

 and that agcordingly the sound emitted directly from the 

 reed, or string, or from the resonance-board in connec- 

 tion with the string, is simple harmonic. On the other 

 hand, it is certain that the note actually heard is com- 

 pound, and capable of being resolved into several com- 

 ponents with the aid of resonators. 



The explanation of this apparent contradiction is very 

 simple. Exactly as in the case of the ordinary free reed, 

 whose motion, as has been found by several observers, is 

 rigorously simple harmonic, the intermittent stream of 

 air, which does not take its motion from the reed, gives 

 rise to a highly compound musical note, whose gravest 

 element is the same as that of the pure tone given by the 

 string and resonance-board. One effect of the string, 

 therefore, and that probably an important one, is to inten- 

 sify the gravest tone of the compound note given by the 

 intermittent stream of air. 



The fact that the pitch of the system is mainly de- 

 pendent upon the string, seems to have distracted attention 

 from the important part played by the stream of air, and 

 yet it is obvious that wind cannot be forced through such 

 a passage as the reed affords without the production of 

 sound. A few very simple experiments would soon decide 

 whether the view I am advocating is correct, but I have 

 not hitherto had an opportunity of making them properly. 

 I may mention, however, that I have noticed on one or 

 two occasions an immediate falling off in the sound when 

 the wind was cut off, although the string and reed re- 

 mained in vibration for a second or two longer. A 

 resonator tuned to one of the principal overtones was 

 without effect when held to the string, but produced a 

 very marked alteration in the character of the sound 

 when held to the reed. 



It will be seen that according to my explanation the 

 principal acoustical characteristic of the string — that its 

 tones form a harmonic scale — does not come into play, 

 the oi'fice of the string being mainly to convey the 

 vibration of the reed itself (as distinguished from the 

 wind) to the resonance-board and thence through the air 

 to the ear of the observer. A second advantage due to 

 the string appears to be a limitation of the excursion of 

 the reed, whereby the peculiar roughness of an ordinary 

 reed is in great measure avoided. 



I should mention that I have not seen anything of the 

 instrument for the last six months, in which time I under- 

 stand great progress has been made. 



Rayleigh 



ICE PHENOMENA IN THE LAKE DISTRICT 



DURING the severe frost at the close of last year, 

 some excellent opportunities were afforded of ob- 

 serving various phenomena in connection with the forma- 

 tion and fracture of large sheets of ice. After the ice had 

 attained a thickness of some inches on Dervventwater and 



* In the mechanical^ not th< 



Bassenthwaite Lakes, the continued cold— with the ther- 

 mometer for several days ei.^^ht or nine degrees below the 

 freezing-point (Fah.), even at mid-day— caused such shrink- 

 age in the ice that cracks of great length were now and 

 then produced with a noise almost like the firing of a small 

 cannon. These cracks frequently passed quite across the 

 lake, and presented many points of interest, especially to 

 the geologist. In some cases two cracks met at an angle, 

 as in Fig. i ; sometimes three cracks radiated from a 

 central point, as we may often see in a cracked plate ; and 

 occasionally one long and wide crack would appear to 

 have shifted others crossing it, just as a fault shifts beds 

 or veins, as in Fig. 2, where the portions were shifted 

 about two inches, and in the same direction in the case of 

 several distinct cross cracks. 



Some of the cracks were so much as two inches wide, 

 and presented curious and interesting vein-structures. 

 One class of crack was vertically veined, presenting the 

 appeanance of a number of thin sheets of opaque ice 

 placed on end close to one another. Such cases reminded 

 me strongly of vertically banded fclstone dykes occurring 

 a little north of Wastwater. Their formation may be 

 explained thus : — The crack when first formed is exceed- 

 ingly fine, but water soon finds its way into it, and 

 freezing quickly, becomes a thin vertical seam of opaque 

 ice. A second and a third opening of the crack occurs, 

 and a new vertical sheet is formed each time. Thus the 

 whole crack becomes filled, as it widens, with successive 

 vein-like sheets of ice. At one spot on Bassenthwaite 

 Lake I observed two of these veined cracks crossing one 

 another, as in Fig. 4 ; the one of less width ran for about 

 one foot in the direction of the other, and then pissed 

 out, maintaining the same general direction as it pre- 

 viously had. Here then was another example of what 

 occurs so frequently among rock-veins, the newer vein 

 conforming for a short distance with the direction of the 

 older, and thus at first sight giving the appearance of its 

 having been shifted by the latter. In this connection 

 compare Fig. 4 with Fig. 2 ; in the latter case the smaller 

 cracks seemed certainly to have been the first formed. At 

 some spots quite a plexus of intersecting cracks were 

 seen, and it was of interest to notice hov/ frequently this 

 combination resembled the faults laid down upon a geo- 

 logical map. 



Another circumstance, suggestive on a small scale of 

 geological phenomena, was the curious way in which the 

 ice for about a mile and a half over the course of the 

 Derwent, as it flowed into Bassenthwaite Lake, was raised 

 into a low and broken anticlinal. For some time after 

 the ice had formed over the greater part of the lake, a 

 fine, first of open water and then of thin ice, followed the 

 river course for some distance, until its waters lost their 

 distinctness in the general body of the lake. In the mean- 

 time, from the dryness of the weather and the continuance 

 of the extreme frost, the ice subsided with the waters, and 

 produced a gentle upheaval over the course of the river, 

 which upheaval, however, seemed generally to have re- 

 sulted in a more or less sharp ridge usually fractured in 

 the direction of its length, and but seldom showing cracks 

 of any size passing quite through from one side to the 

 other. 



Cracks showing a vertically veined structure have 

 already been mentioned ; these seem in all cases to have 

 opened little by little, and to have been quickly filled with 

 successive thin sheets of opaque ice ; they probably never 

 stood open and full of water for any length of time, but 

 were the results merely of the contraction of the ice under 

 the extreme cold. Another class of cracks, however, seem 

 to have been wide and gaping during a thaw, and to have 

 been suddenly sealed up by the freezing of the liquid con- 

 tained between the sides. It is well known that as a 

 general rule the more quickly a body solidifies from a 

 liquid condition the greater the number of cavities— liquid 

 and gaseous— it will contain, the liquid being frequently 



