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Tribune Extras Lecture and Letter Scries. 



north la of great importance, and can be 

 certainly known if wo couid find larger 

 amount." nf bowlders with grooved surfaces. In the 

 gradual elevation of temperature, a-nd a diminution of 

 the magnitude of glaciers, there came a time when the 

 glaciers tliere were local, carrying \vith them tho mate- 

 rial by which it passed this coast, and very probably 

 have left those striated bowlders which could hardly 

 have had any other route than such as I have referred to. 

 I cannot express tuv own immediate degree of satis- 

 faction in welcoming back Dr. B/ssds who has so faith- 

 fully executed the commission we commitr.,^1 to him. 



Dr. Bes.sels replied: I should like to mako another re- 

 mark on the raising- of the land. I thought I might find 

 pome clue in coll-ctins some specimens of the stems of 

 old willows that grew on that land, and on examining 

 those different willow stems, I found that there was not 

 a single onu of them older than 19o years. That is indi- 

 cated by the number of rings, although I do not think 

 that such a rise as l.GOd or 1,800 feet could have been pro- 

 duced in 196 or 200 year.?. 



Dr. Gnyot asked : Will Dr. Bessels please tell us what 

 the diameter of that tree is, which is 196 years old? 



Dr. Bessels These willow stems were a little larger 

 than uiy finger. 



Dr. Guyot Might I ask Dr. Bessels how he would ex- 

 plain in the transportation to the North the coming of 

 the bowlders from Labrador. It seems that the sea 

 ought to have come as low down as Labrador. 



The Chairman (Prof. Henry) Where would be the 

 point of separation between Greenland and the conti- 

 nent! 



Dr. Bessels The point of separation would probably 

 be in the vicinity of Newfoundland, becanse in. tracing 

 such a Hue following the coast of Greenland would just 

 exactly give us the shape of the continent required. 

 You will remember that Burckraeister was the first to 

 point out that such a triangle with the points to the 

 south was the shape of the continent. [Dr. Bessels here 

 drew an imaginary triangle on the blackboard.] The 

 apex of the triangle is pointing toward the south, and in 

 tracing the line from tue south cape o Greenland to the 

 eastern cape of Newfoundland that would just give the 

 triangular shape required by the theory. 



Dr Guyot Tuat is true; but all that space from 

 Smith's Sound ought to be open, in order to give the 

 driit from Labrador. 



Dr. Bessels Most likely, but that is what I wanted to 

 flml out, tliougli wo did not find soundings greater than 

 those iu the low fiords, and we found the lesser deplhs 

 toward the north, the greater toward the south. 



Dr. Gnyot And the separation would bo still in exist- 

 ence <>n i lie nortuern part. 



Dr. Besicls We find the same motion of the earth is 

 existing still in Australia. The liutle continent Austra- 

 lia is tilting jUat nko a boat under a heavy pressure of 

 eca. 



Dr. Gnyot What I want to know is whore was the 

 connection between Greeland and the continent. That 

 is the point, and I think that could not bo anywlieiv 

 than just in the southern part. 



Dr. Besselt Well, I think the last connection must 

 have been somewhere in the latitude of Labrador. 



Dr. Guyot Anyhow, this transportation of drift north- 

 ward is very interesting. All or a part of Bnerinn's 

 Strait would bo open at that time, and the change of 

 separation would interrupt tno currents from the Pa- 

 cific, and change the whole circulation from the Pacific 

 Bea. 

 Prof. Nowherry Wo think the circulation of the soa 



must have changed, because we find that the amount oi 

 atmospheric saturation from existing currents is not 

 enough to form glaciers. 



Dr. Bessels It is so very small that the region under 

 consideration could not have been so affected. 



The Chairman Would not the abnormal appearance 

 >f the drift be explained by simply supposing that tho 

 sea of the North is not coincident with tho pole of the 

 earth 1 



Dr. Guyot Certainly. 



Prof. Newberry I venture to refer to the fact ad- 

 mitted, that wo have traces of the lower Silurian rock 

 stretching through to the utmost point readied north, 

 and the upper Silurian, also. The elevation of these series 

 of later deposits has come lower this way, as you know. 

 In the mouth of the St. Lawrence we have these same 

 deposits 500 feet deep in the sea, and down about New- 

 York on the Hudson, 200 or 250. The depression seems 

 to be greater toward t:ie north. 



The Chairman then announced that tho photo- 

 grapher of the Smithsonian Institution desired to 

 take a photograph of the audience. Thereupon 

 everyhody turned about and faced toward the oppo- 

 site end of the hall. Grave professors ran their fingers 

 through their hair and struck an attitude. A 

 solemn rigidity crept over the spell-bound group, at 

 last to be interrupted by a sigh of relief as the black 

 cloth was finally replaced on the camera. 



The next address was an account of the new 

 instrument at the Observatory. 



THE GREAT TELESCOPE AT WASHINGTON. 



BY PROF. SIMOX NKWCOMB. 



The initiatory movement in the construction 

 of the great telescope was early in July, 1870, when 

 Congress authorized tor it an appropriation of $30,030. 

 The contract was made witu Alvau Clark & Sons of 

 Cambridge, Mass., to manufacture it. Tho price agreed 

 upon for the enure telescope was S1G.03J. Ch.iuce & Co. 

 of England agreed to furniah the glass, they hems: the 

 only makers of achromatic glas* suitable for large re- 

 fractors. There were many failures in casting the glass 

 disks, and fully a year elapsed before Chance & Co. de- 

 livered the glass to the Messrs. Clark; but even this was 

 more expeditious than has been the case in other in- 

 stances, as at least one order given about the same time 

 had not at last accounts been tilled. Alvau Clark & 

 Sons finished tho great telescope in October, 1872. It is 

 not too much to say that the glass fully mot the high 

 hopes that had been entertained concerning it. 



Tho telescope is mounted on what is known as the 

 Gorman, or rather tho Munich plan; but this has not 

 been rigidly adhered to where improvement was pos- 

 sible. Certain important modifications have been made 

 in the machinery by which the instrument is operated; 

 some of these were devised by tho Messrs. Clark, and 

 one was adopted from Mr. Cooke's great telescope at 

 diieshead. As a result of these improvements, the ob- 

 server can point tho telescope by means of the circles 

 alone so nearly that an object sh.ill bo in tho field of 

 view of the finder without the observer havi-m been re- 

 quired to leave tho floor or to look at the object. 



Tho question is 1'requeutly asked. How does the new 

 instrument compare with other telescopes 7 This Is dif- 

 lleult to answer, since there are no refracting telescopes 

 in this country of comparable dimensions. Tho question 

 as to tho comparative efficiency of refracting and re- 

 fioutiut telescopes is frequently raised. It must bead- 



