June 14, 1883] 



NA TURE 



i55 



recent weather in England will perhaps find a grain of 

 consolation in the statement that M. Thollon, who comes 

 every summer to work in connection with this part 

 of the Observatory, spent his whole summer there last 

 year without being able to make a single observation. 

 M. Egoroff, Professor of Physics at Warsaw, was, we 

 learn, occupied during the months of July and August, as 

 i.i preceding yens, with the spectroscopic study of atmo- 

 spheric absorption, working with a beam of electric light 

 sent from Mont-ValeYien to the Observatory. 



Most of our readers are aware that the French Govern- 

 ment has, as we think wisely, determined to separate the 

 special meteorological investigations from the astronomical 

 work of the Observatory., In consequence of this decision, 

 Admiral Mouchez is now making meteorological obser- 

 vations of possibly a still higher value, with the special 

 object of determining the different corrections, such as 

 for refraction, to be applied to the astronomical obser- 

 vations. 



The magnetical observatory which is now being com- 

 pleted will evidently be one of the first order. Six 

 subterranean chambers of constant temperature have 

 been built under the best possible conditions of isolation 

 and stability. An outer wall of nearly 2 m. thickness 

 incloses a rectangular space 40 m. in length, and 14 m. 

 wide, completely impervious to moisture. The observing 

 chambers, of which there are four of 5111. by 4 m., and 

 t vo of 6 m. by 5 m., are constructed in this space, being 

 isolated from its walls by passages 2 m. wide. The walls 

 of the observing chambers themselves are 80 centimetres 

 thick; they communicate with each other by doors 

 Jim. wide, and have a height of 3'65 m. The vaulted 

 rx>f, 1 m. tbic<, is covered by earth to the thickness of 

 2 m., whilst grass and plants protect the soil from the 

 direct rays of the sun, and from frost. The observing 

 clambers can either be lighted by gas or by reflection 

 from without. 



Advantage has been taken of the existence of these 

 chambers by placing in them the clocks from which the 

 t me is distributed throughout Paris, but in spite of all 

 precautions it is unfortunately discovered that the cham- 

 bers are not altogether free from minor trepidations 

 resulting from the traffic of the streets. It is proposed 

 therefore to place the apparatus for the study of the ver- 

 tical and slow movements of the soil to a gallery in the 

 Catacombs 27 m. below the surface. This apparatus has 

 bjen constructed and is ready for use. 



Among the meteorological work to be done with the 

 object to which we have previously referred is included a 

 series of observations from a captive balloon. This is of 

 s ich a sire that with ordinary gas in calm weather it can 

 tike self-registering barometers, thermometers, and hygro- 

 meters up to a height of 500 m., and with pure hydrogen 

 it can ascend to a height of 800 m. It has been found by 

 e <periment that the balloon cannot be well managed if 

 the air has a velocity greater than 4 m. or 5 m. per second : 

 but this is not regarded as being inconvenient, because it 

 is during complete calm that those great and frequent 

 inversions of the law of decrease of temperature which 

 most sensibly interfere with astronomical refraction, 

 manifest themselves. 



Simultaneous observations will be made on the meridian 

 of the Observatory of Paris, north at the Observatory of 

 Montmartre, and south at the Observatory of Mont- 

 souris. 



The construction of the great refractor of 16 m. focal 

 length with its dome of 20 m. in diameter is going on 

 steadily. The object-glass worked by M. Martin is 

 already finished, and the ground on which the Observa- 

 tory is to be built is now prepared. There are some 

 interesting details in the report touching the dome, the 

 dimensions of which we learn will be the same as that of 

 the Pantheon, and the largest ever attempted. 



In insisting upon such a dome turning with ease, it 



must not be forgotten that it would be useless to construct 

 one of such dimensions, unless steps were taken to prevent 

 the ill effects which would arise from any displacement or 

 deformation of the soil on which the Observatory is to 

 be erected, or the walls of the Observatory itself. The 

 arrangement which is to be adopted in the construction 

 of this dome is that proposed by M. Eiffel. In order to re- 

 duce to a minimum the resistance due to friction on circular 

 rollers, M. Eiffel proposes to float the dome by means of a 

 circular caisson plunged in a receptacle of the same form, 

 filled with a liquid which will not freeze, such as an aqueous 

 solution of chloride of magnesium. An experiment made 

 with a small model gave hopes of the most satisfactory 

 results with this arrangement. There is much originality 

 in the idea, and at the Paris Observatory more than an>- 

 where else perhaps it is necessary that some such ar- 

 rangement as this should be adopted, for it must not be 

 forgotten that the Observatory is situated over the Cata- 

 combs, one result of which has been that for many years 

 the pillars of the meridian circle erected in the gardens 

 have gradually inclined towards the east in consequence 

 of the displacement of the soil. If the same thing were 

 to happen to the Observatory for the great equatorial, 

 there is little doubt that before many years were over the 

 dome would be quite immovable, whereas with Eiffel's 

 floating arrangement, whatever be the change in level 

 within season due to such a cause as we have named, the 

 dome would still turn. 



Another point which is engaging the attention of the 

 Director is the erection of an astronomical observatory on 

 the Pic du Midi, at a height of 2859 m. At this elevation, 

 according to General de Nansouty, it is easy to read at 

 night by the light of the stars alone, and fifteen or sixteen 

 Pleiades are visible to the naked eye. It is indeed time 

 that the importance of the possibility of observations at 

 great heights received a fuller recognition. When the 

 astronomical party were in the Rocky Mountains in 1878, 

 to observe the eclipse of the sun there, three American 

 observers had no difficulty in detecting the satellites of 

 Jupiter every night with the naked eye. Nothing could 

 show better the purity and transparency of the air than 

 this, and to establish these facts is to establish also the 

 necessity for utilising them. It is intended that any 

 astronomer who wishes to make any special researches 

 may take advantage of this Pic du Midi Observatory. At 

 the same time, however, astronomers will be sent from the 

 Paris Observatory to profit by the clear skies of the south 

 at those times when the climate of Paris reduces the 

 number of possible observations in the Observatory itself. 

 It is pointed out that not only the science of astronomy, 

 but physics, chemistry, and physiology, will probably 

 derive great benefit from the institution of such an obser- 

 vatory as this. 



NOTES 



The Royal Society Soiree last Wednesday was as successful 

 as usual, though the absence of the president, Mr. Spottiswoodc, 

 through illness, was to be regretted. From inquiries last night 

 we are glad to learn that Mr. Spottiswoode, who is suffering 

 from Roman fever, is going on very well. 



The candidates selected by the Council of the Royal Society, 

 whose names we gave in Nature, vol. xxvii. p. 614, were 

 elected last Thursday. 



Dr. Michael Foster has, in accordance with unanimous 

 expectation, been elected to tbe newly established Professorship 

 of Physiology in the University of Cambridge ; and Dr. 

 Alexander Macalister, F.R.S., Professor of Comparative Ana- 

 toaiy and Zoology in the University of Dublin, has been elected 

 to the Professorship of Anatomy, vacant by the resignation of 

 Prof. Humphry. 



