July 18, 1884.] 



SCIENCE. 



61) 



so-called ' kettle ' moraine. As is well known, 

 chiefly through the work of the author, together 

 with Upham and others, this moraine consists 

 of a series of loops about the Great Lakes, and 

 continuing thence eastward and westward. 

 Commencing with the Green-Bay loop as most 

 typical, the author describes every loop sepa- 

 rately and minutely, taking them in succession 

 going eastward, and then returning and going 

 westward. All we can do here is to trace 

 briefly the course of this moraine as shown in 

 the map, plate xxviii. 



Commencing eastward, this moraine passes 

 through Cape Cod and through Long Island, to 

 New York. This part is often described as 

 the first glacial or limit moraine. If so, the 

 two are here coincident. But possibly the 

 true limit is farther out to sea ; or, more prob- 

 ably, the ice- sheet at its farthest limit ran out 

 here into the sea, and formed no moraine at 

 all, its debris being carried away by icebergs. 

 From New York the two moraines separate, the 

 limit moraine passing through New Jerse}^ and 

 Pennsylvania, where it has been traced by Cook 

 and Lewis ; while the second glacial moraine 

 turns northward into middle New York, passes 

 in a curve around the Finger Lakes, and then 

 southward to join the limit moraine in eastern 

 Ohio. After running together a little way, they 

 again part company, the limit moraine passing 

 along an irregular line a little north of the Ohio 

 River, then crossing the Mississippi and follow- 

 ing the south and west side of the Missouri 

 River into Montana and British America ; 

 while the second moraine turns northward, 

 sweeps about the Great Lakes in a succession 

 of loops, and then, making two more grand 

 loops, — one in Iowa and one in Dakota, — it 

 finally passes along the Coteau of the Missouri, 

 and onward into British America. 



The importance of the work of Mr. Chamber- 

 lin and Mr. Upham, in connection with that of 

 Messrs. Cook, Lewis, and Wright, on the first 

 glacial or limit moraine, in their bearing on 

 the question of the existence of a veritable 

 ice-sheet, cannot be overestimated. 



In the paper on barometric measurements 

 by Mr. Gilbert, a new method of measuring 

 heights is brought forward. The essentials of 

 this method are as follows : — 



For the purposes of observation there are 

 two base stations, one high and one low, the 

 difference in altitude between them being as 

 great as possible, compatible with close verti- 

 cally. At these two stations, only the barome- 

 ter and its attached thermometer are observed, 

 no other instrument being considered neces- 

 sarv. The actual difference in altitude be- 



tween these base stations is determined by 

 spirit-level ; and this constitutes the altitude, 

 — a vertical base-line, by which all other al- 

 titudes are gauged. 



The field-notes consist of barometric read- 

 ings applying "to the upper base station, the 

 lower base station, and the new station, respec- 

 tively. 



The method of computation consists in first 

 correcting the instrumental readings for index- 

 error and temperature. These readings are 

 then collected in groups of three, each obser- 

 vation at a new station being associated with 

 the coincident observations at the base stations. 

 The altitude of the upper base station is then 

 computed as usual, without applying the cor- 

 rections for moisture, temperature, or gravity ; 

 and the height of the new station above the 

 lower base station is calculated in the same 

 way, thus assuming that the air is dry, and has 

 a uniform temperature of 32° F. ; and, these 

 two results being considered approximate, the 

 following proportion is made : — 



Approximate height of base-line : True height of base-line : : 

 Approximate height of new station : True height of new station. 



There is little of importance in this publica- 

 tion that has not appeared previously in some 

 form or other. 



Of course, the method would, in the first 

 place, be limited in its application to a very 

 small horizontal area ; for only in such an area 

 could the conditions of density be similar 

 enough to allow of its use : and the first thought 

 that would strike one would be the compara- 

 tively rare occurrence of the conditions of 

 verticality proposed, though the method cer- 

 tainly has the mark and merit of ingenuity. 



Most of such devices are designed to do 

 away with the influence of the ' hour of the 

 day,' as it is called, or the varying effect of 

 the different conditions of temperature and 

 moisture. Any real control over these ele- 

 ments in the problem must come from the 

 careful noting of all the circumstances under 

 which the data are collected ; and the question 

 can only be decided, if it ever is, by observa- 

 tions continued for a long time. 



The only great effort to secure the data for 

 this ' horary ' correction was made by Plan- 

 tamour, in his discussion of the forty-year 

 series of observations carried on between 

 Geneva and the St. Bernard hospice : x but this 

 series only covers one of the many conditions 

 under which such measurements ma}' be made, 

 for decided differences would be introduced by 

 unequal insolation along mountain chains, near 



1 Mem. Soe. phj-s. Geneve. 



