June 14, 1894] 



NA TURE 



149 



I 



this fissure, on it cooling down, will be kneaded by mastication 

 articles of irritating food and drink, which will lead to caries 

 round it. The progress of this may erode a segment of the 

 tooth, or at last penetrate into the cavity and the pulp, and 

 lead to inflammation and abscess ; and none is a more virulent 

 agent in doing this than hot tea. The simmering kettle may be 

 seen on the hob*^ of the kitchen fires in the houses of the working 

 classes in Yorkshire and Lancashire, who are much subject to 

 caries of the 'eeth and dyspepsia, in con^equrnceof the frequent 

 imbibition of its hot contents all day. W. G. Black. 



Edinburgh, May 17. 



The Lowell Observatory, Arizona. 



I LEARN — although I have not myself yet seen the note — that 

 Nature has been unwittingly led into the error of stating that 

 Lowell Observatory, at Flagstaff, Arizona, is a branch of 

 Harvard College Observatory. This impression had its origin 

 in a press dispatch, and I am, with the approval of Mr. 

 Lowell, correcting these wrong impressions when possible. 



Mr. Percival Lowell — whose father is trustee of the Lowell 

 Fund from which the cost of the Lowell Institute Lectures is 

 defrayed — ishimsell an author( "Japanese Art and Customs")and 

 a man of scientific training. He has himself worked out the 

 plan for his observatory work, and will personally supervise and 

 direct the investigations. His institution is one of magnitude, 

 having 18 in. and 12 in. telescopes, and he is justly entitled to 

 the credit. The misunderstanding seems to have arisen from 

 the fact that he has employed two of the Harvard College 

 Observatory assistants for the season, they having been granted 

 leave of absence. I enclose Mr. Lowell's own statement, pub- 

 lished yesterday, being his paper liefore the Boston Scientific 

 Society, and really the first public official statement. 



May 26. John Ritchie, jun. 



[The following description is from the enclosure referred to 

 by Mr. Ri'.chie. We are glad to render Mr. Lowell the credit 

 due to him. — Ed.] 



The Lowell Observatory, the construction of which is now 

 almost completed, is situated in the territory of Arizona, near 

 the town of Flagstaff, in longitude 1 1 2° west, latitude 35° north, 

 at an elevation of 7300 feet above the sea. Its site is thus the 

 highest of any large observatory in the northern hemisphere, the 

 next in point of elevation being the observatory at Denver, 

 5400 feet. In latitude it is furthermore the most southerly of 

 those north ot the equator. But the chief advantage hoped for 

 from its position is in the way of atmospheric conditions, the 

 singularly dry and clear climate of Arizona commending itself 

 to astronomical purposes. 



The observatory buildings stand upon the eastern end of a 

 spur of high land, which rises just to the west of the town and 

 is connected at the back some fifteen miles away with the San 

 Francisco Mountains that reach to a height of 12,500 feet. The 

 buildings are thus protected from the north. To the east and 

 south they overlook the town and the plain beyond, being about 

 300 feet above Flagstaff and a mile away from it in an air line. 

 The hill and the surrounding country are covered in part by a 

 sparse growth of limber. Trees about an observatory are 

 usually considered an advantage, as such vegetation reduces the 

 radiation from the ground and lends to equalise the daily 

 extremes of temperature, thu> giving steadier seeing. The land 

 for the site has very generously been given by the town, and a 

 road to the observatory is being built by the town at its own 

 expense. 



The buildings consist of the equatorial building and of the 

 study, placed at a short distance away from it to leeward of the 

 prevailing winds. This disposition of the buildings is in order 

 to minimise the risk from fire, a serious matter in so isolated a 

 situation. 



The dome of the equatorial building is constructed on a 

 system of parallel arches, after a design by Prof W. H. Picker- 

 ing, who has made a study of domes here and abroad. It is 

 built of a framework upon which rests a cage of wire-netting, 

 and over this is stretched a covering of canvas. One of 

 the chief features of the dome is its lightness. -Mthough it 

 is thirty-four feet in diameter, the whole revolving hemisphere 

 weighs but two tons. Some idea of its lightness and of the 

 ease of moving it in consequence may be got by comparing it 

 with the dome of the large equatorial at Harvard, which, though 

 four feet smaller, weighs fourteen tons, or seven times as much. 

 The whole revolves on the wheels of a live-ring. The dome 



NO. 1 285, VOL. 50] 



was built here and, together with the pier, shipped out in pieces 

 to Arizona. The study building will contain a general or 

 reception room, two sleeping rooms, a photographic room and 

 a tool-room. 



The telescopic equipment consists of three telescopes of 18 

 inches, 12 inches and 6 inches aperture, respectively. The 

 18-inch glass is by Brashear, and is the largest objective Mr. 

 Brashear has yet finished. Its focal length is 26 feet 4 inches. 

 This is an unusually long focus, and length of focus is an advantage 

 in an objective. It and the 12-inch one of Clark's are mounted 

 in twin. The l8-inch will be used for usual and spectroscopic 

 purposes, while the 1 2-inch will be chiefly employed photo- 

 graphically. The third glass, the 6-inch, is also by Clark, and 

 is a fine objective. It has already done good work at Flagstaff 

 by being the first of those in the northern hemisphere to catch 

 the Gale comet the other day. Incidentally, it is a far travelled 

 telescope, having been safely half round the world and back 

 again before ever it started for Arizona. It is of the same size 

 and quality as the one with which Burnham made himself the 

 first of double-star observers. By the ingenuity of Mr. Clark 

 it is mounted portably in equatorial, being thus rendered the 

 largest of small telescopes, or the smallest of large ones, at 

 pleasure. 



The 18-inch has been carefully fitted by Mr. Brashear with 

 various ingenious contrivances by Prof Pickering for photo- 

 metric and spectroscopic work. For micrometrical purposes, 

 in addition to the micrometer proper, he has also had prepared 

 plates minutely ruled, dotted and designed and then diminished 

 by photography, to be introduced beside the image in the tele- 

 scope, for direct comparison with the canals and lakes of Mars 

 and other similar purposes, thus furnishing a second method for 

 micrometrical measurement of such detail. 



The BerthoUet-Proust Controversy and the Law of 

 Definite Proportions. 



In his able address at the annual meeting of the Chemical 

 Society, the President spoke of chemical text-books somewhat 

 scornfully. While I confess that I am not prepared to regard 

 these books as "soul-destroying,'' one and all, I have long 

 felt at least that the dogmatic exposition of the elementary laws 

 of chemistry to which they have accustomed us is most un- 

 satisfactory, and that a critical re-statement of first principles is 

 much needed. To deal with ihe subject fully, would carry 

 me far beyond the limits of a letter to Nature ; but 

 it is proposed in the following communication to draw attention to 

 certain serious misconceptions which have crept into modern 

 text-books with regard to the Berthollet-Proust controversy and 

 the Law of Definite Proportions, and to attempt to re-define 

 somev/hat more accurately the points which were at issue. 



BerthoUet, it is said in the text-books, held that the compo- 

 sition of a compound was not rigidly constant, while Proust 

 showed that " the same chemical compound always consists of 

 the same elements combined in the same proportions by 

 weight," (a statement to be referred to later, as statement A) ; 

 and this statement is regarded as an enunciation of 

 the Law of Definite Proportions, against the accept- 

 ance of which BerthoUet strove so hard. As a matter of 

 fact it seems unlikely that BerthoUet would have felt in the 

 least inclined to contradict the statement quoted. He did 

 not suppose for a moment that it ~*vas possible for two substances 

 to exist which should be sufficiently alike in properties for them 

 to be called the same chemical compound, and yet for these to 

 differ sensibly in their quantitative chemical composition; yet 

 this is what a denial of statement A amounts to. On the con- 

 trary, BerthoUet, like Proust, held the opposite view, namely, 

 that the physical properties of substances are necessarily cor- 

 related with their chemical composition, and therelore that two 

 substances differing in their chemical composition have in general 

 different properties and are not called by the same name. We 

 find BerthoUet making use of this view, for instance, in the 

 course of an argument given in the " Kssai de Statique 

 Chimique," vol. i. p. 346. For he says in effect that if in 

 certain cases we only find compounds of which the constituents 

 are united in ratios, such as .r :^' or a- : )■,, among the infinite 

 number of compounds of these constituents capable of existing, 

 it is just because these combination-ratios correspond precisely 

 to some physical properly (e.g. insolubility) which renders the 

 resulting substance easy of isolation, and takes it (to use the 

 terminology of the time) beyond the reach of the chemical forces 

 which caused its formation. 



