398 



NATURE 



[August 23, 1 8S; 



aurora borealis, but without success. Thus, not even by 

 using the most sensitive English ' dry ' plates, and exposing 

 them from five to seven minutes, have I obtained a trace 

 of a negative. The cause of this is, I believe, the ex- 

 ceedingly limited substance of light possessed by the 

 aurorae ; were thus the entire heavens flooded by the 

 most intense auroras their aggregate lighting power would 

 not equal that of the moon when full. I may therefore 

 assume that to photograph the aurora borealis is an 

 impossibility." 



On a later occasion Dr. Tromholt informs us that he 

 obtained no negative of the aurora borealis throughout 

 his stay at Kautokeino, while he found also, on visiting 

 Bossekop and Sodankyla, that neither had any been 

 obtained at these observatories. 



As to the results of Dr. Tromholt's researches on the 

 aurora, we may add that, as soon as he has received 

 certain comparative tables of the observations made at 

 Sodankyla from Prof. Lemstrom, he will immediately 

 communicate the same to Nature. In the beginning of 

 October next the intrepid savant starts for North Iceland, 

 which he has chosen as his station for the coming winter. 

 He will here chiefly experiment with the ''utstromnings" 

 apparatus invented by Prof. Lemstrom for producing an 

 "artificial" aurora borealis. 



We hare also received from Dr. Tromholt an excellent 

 photograph, taken by himself, of the Circumpolar Obser- 

 vatory which Norway, participating in the programme of 

 international Polar research, has established at Bosse- 

 kop, in North Finmarken. The station is situated on an 

 eminence by the Alten Fjord, and the photograph shows 

 clearly the various huts, Sec, erected for meteorological, 

 astronomical, and terrestrial observations. 



ALDABRA ISLAND TORTOISES 

 '"T'HE following report by the Hon. W. Littleton, ad- 

 ■*• dressed to Sir John Pope Hennesy, Governor of 

 Mauritius, has been forwarded by His Excellency in 

 answer to a memorial presented by the late President of 

 the Royal Society, and several other gentlemen, relative 

 to the preservation of the gigantic tortoises on the Island 

 of Aldabra : — 



Memorandum on Aldabra Island Tortoises 



To His Excellency the Governor,— With reference 

 to your Excellency's request for a report on the Aldabra 

 Island tortoises lately placed on Flat Island, I have been 

 able to get very little information about them. 



The Mauritius Acclimatisation Society recently handed 

 over six tortoises to this Government, on condition that 

 they should be placed on Flat Island and taken care of. 

 The Government accepted the charge, and they were 

 accordingly placed there about two months ago. The 

 Storekeeper-General (Mr. Schmidt), who is much in- 

 terested in them, tells me that they are completely at 

 liberty, that they feed themselves, and are apparently 

 doing well. 



Only five of them are Aldabra tortoises ; the sixth is 

 from Madagascar. They are all young, and of compara- 

 tively small size. 



But I may perhaps mention here that there are several 

 specimens of the Aldabra tortoise, besides these, both 

 here and in Seychelles. There is the well-known large 

 one in the garden of the Royal Artillery mess in Port 

 Louis. He was here before the English occupation of 

 Mauritius in 1S10. The largest circumference of his 

 shell measures 9 feet 3 inches. He stands 2 feet 6 inches 

 high. 



In the Botanical Gardens at Pamplemousses there are 

 two belonging to Mr. Cockburn Stewart, who brought 

 them from Seychelles. They are about ten years old. 

 The largest circumference of their shell is 7 feet 2 inches, 

 and they stand 1 foot 8 inches high. Mr. Schmidt tells 



me of a very large one belonging to Mr. Castel, at 

 Riviere Seche, and of a very large pair on the estate 

 " Mon Tresor," near Mahebourg, belonging to Mr. 

 Daruty ; but their measurements, which have been 

 promised to me, I have not yet received. 



A considerable number are kept by various people ot 

 Seychelles, including a pair at Government House, Mahe", 

 the female of which recently laid eggs, and I am told 

 that many of the tortoises kept on the Seychelles Islands 

 frequently breed. 



1 am sorry not to have been able to collect for your 

 Excellency's information more details of these creatures ; 

 but I have stated enough to show that there are many 

 specimens well known and in good keeping. 



I have also been unable to ascertain whether there are 

 any of large size known to remain on Aldabra Island ; 

 but I am told that it is supposed there are in the thick 

 scrub of the interior. 



(Signed) W. LITTLETON 



Colonial Secretary's Office, Port Louis, 

 7th July, 1S83 



THE METEOROLOGY OF THE ARCTIC AND 

 SUBARCTIC PORTION OF THE ATLANTIC 

 OCEAN 1 



UP to the publication of this work by Prof. Mohn, our 

 knowledge of the diurnal meteorological phenomena 

 of this important part of the ocean was nearly altogether 

 a blank. The intere^ing results here detailed are de- 

 duced from three series of hourly observations made 

 during the Norwegian Expeditions in the summers of 

 1876, 1 S77, and 1878, which Prof. Mohn organised and 

 carried out with a skill and a completeness that leave 

 nothing to be desired. The new facts thus brought be- 

 fore us largely extend our knowledge of the physics of 

 this portion of the North Atlantic. 



The diurnal phenomena de.ilt with are atmospheric 

 pressure, temperature, and aqueous vapour, the force of 

 the wind, and the temperature of the surface of the sea. 

 Of these the discussions of the atmospheric pressure and 

 temperature are the most important and satisfactory. 

 The results of the atmospheric pressure present several 

 points of the highest interest. The general curve for the 

 three seasons, if a scarcely perceptible dip about 8-9 p.m. 

 be neg'ected, shows only one minimum at 4 a.m. and one 

 maximum at 2 p.m., thus roughly approximating to the 

 curve of temperature. The curves for the separate 

 seasons 1876 and 1878 exhibit an evening minimum with 

 greater distinctness. The observations made by the 

 Challenger Expedition in the Antarctic Ocean give a 

 curve with only one minimum early in the morning and 

 one maximum early in the afternoon ; and it is highly 

 probable that if the observations made by the Nor- 

 wegian Expeditions quite in the open Atlantic were alone 

 included, the resulting curve would give no sign of a dip 

 in the evening. 



Prof Mohn then examines the observations made at 

 the stations on the coast of Norway at 8 a.m., 2 p.m., and 

 8 p.m., and it is concluded that the diurnal variation of 

 the barometer during the summer months on the adjacent 

 coasts of Norway, as well as in the Norwegian Sea, has 

 its minimum in the morning and its maximum in the 

 evening, and that possibly there is a tract in the Nor- 

 wegian Sea including the bounding coasts of Norway and 

 Greenland, thence crossing Iceland, and passing to the 

 west and south of Faroe, where the lines of barometric 

 variation would represent values with plus signs instead 

 of minus signs as elsewhere. In other words, over this 

 region there occurs a state of things the reverse of what 

 obtains over the lower latitudes of the ocean and the land 



1 " The Norwegian North Atlantic Expeditions 1876-78. Meteorology." 

 By H. Mohn. With 13 woodcuts and 4 plates. (Christiania, 1883.) 



