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Government for about half the amount which he could have obtained from other tenants. To Logan also, McGill University owes much; for, in 1864, he founded and endowed the "Logan Gold Medal" for an honor course in geology and natural science, and, in 1871, gave $19,000, which, together with $1,000 given by his brother, the late Mr. Hart Logan, forms the endowment of the "Logan Chair of Geology."

Since resigning his position as Director of the Geological Survey, he has carried on explorations at his own expense, and, at the time of his death, arrangements had been nearly completed for putting down a bore-hole in the Eastern Townships, at a cost of $8,000; as he thought that this would enable him to prove the truth of his views with regard to the age of the metamorphic rocks there.

Sir William was the first to give us any definite information about those wondrous old Laurentian rocks which form the backbone of our continent. He showed us that they were older than the Huronian, and that they consisted of a great series of metamorphosed sedimentary rocks, which are divisible into two unconformable groups, with a combined thickness of not less than 30,000 feet. The great beds of limestone which he found in the lower series, the plumbago, the iron ores, the metallic sulphurets, all seem to point to the existence of life in the Laurentian days; but the discovery of Eozoon Canadense made conjecture give place to certainty. Now we know that the world of that far-off time was not a lifeless world. Life, whatever that may be, had been joined to matter.

The first specimens of Eozoon were found by Dr. James Wilson, of Perth; but at the time of their discovery were regarded merely as minerals. In 1858, however, Mr. J. McMullen, of the Geological Survey, discovered other specimens, the organic origin of which so struck Sir William that in the following year-four years before their true structure and affinities were determined by Dawson and Carpenter he even exhibited them as fossils at the meeting of the American Association.

In widely extending our knowledge of the early geological history of the earth, Sir William has done a great work; indeed this may be regarded as his greatest work. Its importance has everywhere been recognized, and the name Laurentian, which he chose for the rocks at the bottom of the geological scale in America, has crossed the Atlantic, and is now applied to the homotaxial rocks of Europe. Sir Roderick Murchison, who dedicated the fourth edition of "Siluria" to Sir William Logan, even substituted Laurentian for "Fundamental Gneiss," the name which he had given to the rocks of the West Highlands of Scotland. "I at first," says Murchison, "termed them 'Fundamental Gneiss,' and soon after, following my distinguished friend

Sir William Logan, I applied to them his term, Laurentian,' and thus clearly distinguished them from the younger gneissic and micaceous crystalline rocks of the Central and Eastern Highlands, which were classed as metamorphosed Lower Silurian."

Logan was not a voluminous writer, and during the later years of his life writing was a great effort to him. Occasional papers from his pen have appeared in the Transactions of the Geological Society of London, in the Canadian Naturalist and the Canadian Journal, and some of these have already been referred to; but most of what he has written is to be found in the Reports of Progress annually submitted to the Government, and in that invaluable book, the Geology of Canada, which is, to a large extent, a digest of what is contained in the reports published previous to 1863. He sometimes expressed himself quaintly, but everything he wrote is clear and exceedingly concise.

In addition to being a Fellow of the Royal Society and of the Geological Societies of London and Paris, he was a member of numerous other learned societies both in Europe and America. At the time of his death, and for many years previous, he was one of our Vice-Presidents; but though frequently solicited to accept the office of President, he always declined, not on account of any lack of interest in the Society, but he felt his time was too fully occupied to permit of his successfully discharging the Presidential duties. We have already alluded to some of the medals which were awarded to him; but it may be mentioned that altogether he was the recipient of more than twenty, including two from the Royal Society.

And now, in concluding, let me say to you, my friends, if you would do honor to the memory of that noble old man, who fought so long, so bravely, for his country, for science, for you, then honor the cause for which he fought: strive with all your might to advance the interests of that cause, and to raise up a superstructure befitting the solid foundation which Logan has laid. He himself even hoped to build the superstructure; but his anticipations were not realized, for life was not long enough, and we must take up the mantle which he has dropped.

B. J. HARRINGTON.

ART. VII.-On Recent Researches in Sound; by WM. B. TAYLOR.

[Continued from page 41.]

IV.

THE Communication of Professor Reynolds "On the Refraction of Sound by the Atmosphere," is in two parts; the first of which considers "The effect of Wind upon Sound," and the second part "The effect of variations of Temperature." The experiments were all made in "a flat meadow of considerable extent;" and the apparatus employed "consisted of an electrical bell mounted on a case containing a battery. The bell was placed horizontally on the top of the case, so that it could be heard equally well in all directions; and when standing on the ground, the bell was one foot above the surface." An anemometer was also used to determine the velocity of the wind. (Proceedings of the Royal Society; republished in the L. E. D. Phil. Mag., for July, 1875, vol. 1, p. 67.)

The experiments were made on four different days, the 6th, 9th, 10th, and 11th of March, 1874; and on the last two days the ground was covered with snow, which furnished an opportunity of comparing the effect of different surfaces on the range of Sound. Additional experiments were made on the 14th of March.

[1.] "On all occasions the effect of wind seems to be rather against distance than against distinctness. Sounds heard to windward [that is against the wind] are for the most part heard with their full distinctness; and there is only a comparatively small margin between that point at which the sound is perceptibly diminished, and that at which it ceases to be audible.' (Phil. Mag., p. 63.)

[2.] The sound of the alarm-bell was always heard "farther with the wind than at right-angles to its direction; [contrary to the old observation of De La Roche in 1816,-which was obviously an exceptional one;] and when the wind, was at all strong, the range with the wind was more than double that at right angles. With the wind, over the grass the sound could be heard 140 yards, and over the snow 360 yards, either with the head lifted or on the ground; whereas at right-angles to the wind, on all occasions the range was extended by raising either the observer or the bell." (p. 68.)

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[3.] When the wind was light the sound beyond the distance of 20 yards, was much less audible at the ground than a few feet above it; and when inaudible in every direction at standing height, the sound could be distinctly recovered by mounting a tree. The same result was obtained by raising the alarm-bell

upon a post 4 feet high; which while materially increasing the range of the sound-even in the direction of the slight wind, in all other directions doubled the range. This is explained by Professor Reynolds, by the continual waste and destruction of the sound waves which pass along the rough surface of the ground or grass, causing the waves immediately above to diverge continually downward, to be in like manner absorbed ; the effect of which is to gradually weaken the sound more and more, as the waves proceed; so that even "when there is no wind, the distant sounds which pass above us are more intense than those we hear." (p. 68.)

[4.] Whatever therefore tends to gradually bend downward the sound rays will increase their sensible range. Professor Reynolds found by observations with the anemometer that the velocity of the wind increased from the ground upward; (pp. 63, 64) and hence it must give greater rapidity to the upper portion of the sound waves in the direction in which it is blowing and cause their impulses to continually tip downward. "This was observed to be the case on all occasions. In the direction of the wind when it was strong, the sound could be heard as well with the head on the ground as when raised, even when in a hollow with the bell hidden from view by the slope of the ground; and no advantage whatever was gained either by ascending to an elevation, or raising the bell." (p. 68.)

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[5] Elevation was found to affect the range of sound against the wind in a much more marked manner than at rightangles. Over the grass no sound could be heard with the head on the ground at 20 yards from the bell, and at 30 yards it was lost with the head 3 feet from the ground, and its full intensity was lost when standing erect at 30 yards. At 70 yards when standing erect the sound was lost at long intervals, and was only faintly heard even then; but it became continuous again when the ear was raised 9 feet from the ground, and it reached its full intensity at an elevation of 12 feet." (p. 69.) The same results were obtained with snow on the ground, excepting that the sound was heard somewhat lower, being less dissipated or absorbed by the surface contact. At 160 yards the bell was inaudible even at an elevation of 25 feet, and the sound was supposed to be hopelessly lost; but at a further elevation of 33 feet from the ground, it was again heard; while at 5 feet lower it was lost. At the proper elevation the sound appeared to be as well heard against the wind as with it, at the same distance. These last two observations very strikingly correspond with and confirm the observations of Henry [3], and [4].

[6.] "The least raising of the bell was followed by a considerable intensifying of the sound;" and while it could be heard only 70 yards when resting on the ground, (i. e., one foot

high), when set on a post 5 feet high, it could be heard 160 yards, or more than twice the distance, the sound-beams evidently rising faster at or near the ground, than they do higher up. (p. 69.) "The intensity of the sound invariably seemed to waver, and as one approached the bell from the windward side, the sound did not intensify uniformly or gradually, but by fits or jerks." This is supposed to be the result of the more or less curved sound rays crossing each other at a small angle and producing an "interference." (p. 70.)

A subsequent experiment was made on the 14th of March, during a strong west wind, its velocity at an elevation of 12 feet being 37 feet per second, at 8 feet, 33 per second, and at one foot from the ground (there being no snow on the grass) 17 feet per second. While the results as to varying range fully confirmed the previous experiments, the raising of the bell caused the sound to be heard even better against the wind than in the direction of the wind. (p. 71.) This curious circumstance is explained by Professor Reynolds as "due to the fact that the variation in the velocity of the air is much greater near the ground, than at a few feet above it;" and "when the bell is raised the rays of sound which, proceed horizontally will be much less bent or turned up than those which go down to the ground; and consequently after proceeding some distance these rays will meet or cross, and if the head be at this point they will both fall on the ear together, causing a sound of double intensity. It is this crossing of the rays also which for the most part causes the interference" just mentioned. (p. 71.)

Professor Reynolds concludes that "these experiments establish three things with regard to the transmission of sound: 1. That when there is no wind, sound proceeding over a rough surface is more intense above than below. 2. That as long as the velocity of the wind is greater above than below, sound is lifted up to windward and is not destroyed. 3. That under the same circumstances it is brought down to leeward, and hence its range extended at the surface of the ground. These experiments also show that there is less variation in the velocity of the wind over a smooth surface than over a rough one. It seems to me that these facts fully confirm the hypothesis propounded by Prof. Stokes; that they place the action of wind beyond question; and that they afford explanations of many of the anomalous cases that have been observed." (p. 71.)

[7.] In regard to the second part of the communication, treating of the effect of Temperature differences in refracting sound, Professor Reynolds shows that as "every degree of temperature between 32° and 70° adds approximately one foot per second to the velocity of sound," there must necessarily be an upward flexure of the rays, whenever by reason of any consid

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