376 



NATURE 



[February 17, 1898 



dykes radiate from the lake, putting through the older lavas as 

 exposed on the inner slope. The inner slope appears to have 

 been formed by fracture, and not by flow. The old crater did 

 not occupy the whole extent of the piesent caldera ; if it had 

 done so the lava would have overflowed at the lowest part of 

 the rim, but the whole rim is formed of lava-flows from some 

 higher and now vanished centre. One very remarkable feature 

 of the geology is the strong glaciation of the rim, shown by well- 

 marked striae and great morainic deposits. There are traces of 

 glaciers radiating down the slope, in some cases to a distance of 

 five miles. There is evidence of volcanic activity during the 

 glacial period ; on one of the peaks of the rim an ice- 

 planed surface of old lava is covered by two layers of pumice 

 separated by a flow of rhyolite. The severe floods, which must 

 have accompanied eruptions at that period, would account for the 

 vast masses of sediments which fill the radiating valleys. The 

 observed phenomena can only be accounted for by the presence 

 of a great volcanic peak covering the present area of the lake, 

 and sweeping upward as a continuation of the present outer 

 slopes. The probable history of this mountain is summarised 

 thus : — 



The history of Crater Lake and its rim began in the up- 

 building, by normal volcanic processes, of a large volcano — to 

 which the name Mount Mazama is given — comparable in the 

 nature of its lavas and in its structure and size with the greater 

 peaks of the Cascade Range. This volcano was active in the 



the rim of Crater Lake — a frog, a snake, and a salamander. 

 By the use of tow-nets several minute algae were found in the 

 water, and many minute Crustacea, of which Daphnis pulex 

 pidicaria was the commonest. Several larval insects, a leech, 

 a species of Gordius, and one species of mollusc, an undetermined 

 Physa, were also found. No fish could be discovered, but an 

 attempt to introduce trout is to be made. 



Dr. Merriam gives an elaborate classification of the life-zones 

 on Mount Mazama, and a complete list of all the animals 

 found ; an extensive flora is also published, and in all respects 

 the special number of Mazatiia is highly creditable to the Society 

 which has produced it. The Mazamas are to popularise the lake 

 for the use of tourists by introducing various attractions, which 

 we fear will detract from its present charm by destroying the 

 absolute wildness of the whole surroundings. H. R. M. 



ADDRESS TO THE ROYAL ASTRONOMICAL 

 SOCIETY} 



T T is the duty of your President at this annual meeting of our 

 Society to address you on a very important subject. I 

 allude, of course, to the award of the Gold Medal which is 

 annually conferred by the Royal Astronomical Society on some 

 astronomer who has rendered signal service to our science. The 

 discharge of that duty is, perhaps, the most responsible official 

 act which devolves on the occupant of 

 this chair during his tenure of the dis- 

 tinguished position of President. I am to- 

 set forth the ground upon which on the 

 present occasion the medal has beerv 

 awarded by "your Council to our distin- 

 guished Fellow, Mr. W. F. Denning. 



The contributions of Mr. Denning ta 

 astronomy may be ranged under three 

 heads. 



( 1 ) Discovery of Comets. 



(2) Observation of Planetary Pheno- 

 mena. 



(3) Researches on Meteors. 

 It will be convenient for me to describe 



his work in these three different depart- 

 ments in the order just given. The first 

 and second departments must, however, 

 be treated with comparative brevity, for 

 it is on the third department that your 

 Council laid special stress in making their 

 award. 



(i) Comets. 



Fig. 2. — Crater Lake, showing Wizard Island. 



glacial period, lava and glaciers combining to mould its form. 

 Somewhere near its final eruption, and perhaps in consequence 

 of the rapid draining away of lava by the small cones near the 

 base of the mountain, the molten material from the interior was 

 withdrawn, the summit of Mount Mazama collapsed and sank 

 away, leaving a huge gulf measuring six miles by four, and about 

 4000 feet deep. Volcanic activity continued on the floor of the 

 caldera for some time ; but since rainfall is in excess of evapora- 

 tion in that region, water gradually accumulated to form the 

 present Crater Lake. 



The water of the lake is remarkably transparent, free from 

 any visible organic matter, and fresh to the taste, but no analysis 

 of its saline contents seems to have been made. The tempera- 

 ture of the water when examined in August 1896, averaged 

 about 60° F. on the surface. The deep- temperature, taken by 

 means of a Negretti and Zambra reversing thermometer in the 

 unsatisfactory Magnaghi frame, was reported as 39° at 555 feet, 

 41° at 1040 feet, and 46° at 1623 feet. If these figures were 

 trustworthy, it would appear that the water in Crater Lake still 

 derives heat from the rocks ; but if this interpretation is correct, 

 it is difficult to account for the minimum at the maximum 

 density point, unless indeed the water is saline enough to have a 

 maximum density point perceptibly lower than that of fresh 

 water. Dr. Evermann, of the U.S. Fish Commission, who 

 made the observations, does not seem to have entire confidence 

 in their accuracy. 

 - Only three species of invertebrates were found living within 



NO. 1477, VOL. 57] 



Each year usually brings the announce- 

 ment of certain new comets, the discovery 

 of such objects being the rewards of those 

 observers who patiently scan the heavens, evening after evening 

 and morning after morning, with the particular object of de- 

 tecting these shy visitors to our skies. Mr. Denning has been 

 one of those who have engaged in this work, and his success has 

 been noteworthy. The following list gives the designations of 

 five comets which have been discovered by our medallist. 



Comet 1881 V. Period, 8-68 years. 



Comet 1890 VI. 



Comet 1891 I. 



Comet 1892 II. 



Comet 1894 I. Period, 7*3 years. 



While searching the skies for comets, Mr. Denning has not 

 unfrequently discovered nebulae which had escaped the attentioii 

 of previous observers. No fewer than twenty new nebulae have 

 thus been added by Mr. Denning to the lists of those already 

 known. Most of these new objects lie in the vicinity of the • 

 North Pole. 



(2) Planetary Observations. 



A striking characteristic of Mr. Denning's work is the 

 methodical accuracy with which he has carried through what- 

 ever astronomical research he has in hand. Mr. Denning never 

 spared himself any pains in the efforts necessary to give his work 

 the inestimable charms of thoroughness and precision. This 

 may well be illustrated by his planetary observations. We here 



1 Delivered on February 11 by the President, Sir Robert Ball, on the 

 occasion of the presentation of the Gold Medal to Mr. W. F. Denning. 



