June 21, 1888] 



NA1URE 



179 



stantly coalesce and become one (Fig. 9), and so act as 

 a delicate electroscope. When one bubble is within the 

 other, the outer one may be pulled out of shape by 

 electrical action, and yet the inner one is perfectly screened 

 from the electrical influence, thus showing in a striking 

 manner that there is no electrical force within a conductor 

 not even as near the surface as one side of a soap-film is 

 near the other ; for though the force outside is so great 

 that the bubble is deformed, yet the fact that the inner 

 one remains separate shows that the force within is too 

 small to be detected. One of the experiments described 

 shows at the same time the difference between the 

 behaviour of two bubbles, one blown inside a third, and 

 the other brought to rest against the third from the out- 

 side. Under these conditions, if electricity is produced 



Fig. 



Fig. 10. 



in the neighbourhood, the two outer bubbles become one, 

 and the inner one, unharmed, rolls down and rests at the 

 bottom of the now enlarged outer bubble (Fig. 10). 



One experiment is described in which a cylindrical 

 bubble is blown with oxygen gas between the poles of an 

 electro-magnet. If the length is properly adjusted, the 

 bubble breads into two directly the exciting current is 

 turned on, though the force due to the magnetic nature 

 of oxygen is so feeble that not the slightest change of 

 shape can be detected in a spherical bubble under the 

 same conditions. 



For other experiments and for details, readers are 

 referred to the original paper in the Philosophical 

 Magazine, the editor of which has kindly allowed us to 

 reproduce the illustrations used in this article. 



THE PARIS OBSERVA TORY. 



THE Annual Report of the Paris Observatory, which 

 has recently appeared, draws special attention to 

 the two events which have rendered the past year 

 memorable, not merely in the history of the Observatory, 

 but in that of astronomical science as a whole. The first 

 of these was, of course, the meeting at Paris of the Inter- 

 national Congress for the execution of the photographic 

 chart of the heavens, and Admiral Mouchez gives the 

 names of the members of the Congress, and the resolu- 

 tions adopted by them. Of the Permanent Committee 

 appointed by the Congress, Admiral Mouchez is himself 

 the President, and he has already issued the first number 

 of the Bulletin ale la Carte du Ciel, future numbers of 

 which will be brought out by the Committee as occasion 

 may require. Twelve Observatories, including that of 

 Paris, had definitely pledged themselves to join in the 

 scheme, and five or six more expected to be able to do so 

 shortly, so that there should be no difficulty in completing 

 the chart within three or four years. The International 

 Exhibition to be held at Paris next year would furnish a 

 good opportunity for the reassembling of the Permanent 

 Committee in order that the final decisions relating to 

 the carrying out of this great scheme might be formed. 



The other great event was the publication of the first 

 two volumes of the great Paris Catalogue, the revision of 

 the Catalogue of Lalande. This last work, which has 

 already been referred to in Nature (vol. xxxvii. p. 569), 

 was commenced in 1855, but owing to many unfavourable 

 circumstances has only been pushed forward vigorously 



during the last ten years, and now is all but completed. 

 As the stars which still require observation have become 

 fewer and more scattered, it has been found no longer 

 necessary to devote more than one instrument to the 

 work ; the great meridian instrument has therefore been 

 set apart for this work, and for the observation of minor 

 planets and comparison stars, whilst the other meridian 

 instruments have been left free for the careful study of 

 the places of fundamental stars and for special researches. 

 The " garden " circle has accordingly been used for the 

 observation of circumpolars after M. Loewy's plan, and 

 the Gambey mural circle by M. Perigaud for the re- 

 determination of the latitude of the Observatory. The 

 value found for this latter by a series of consecutive 

 observations of Polaris at upper and lower transit is 

 48 50' i2''"o,but Admiral Mouchez considers that despite 

 the care and skill of M. Perigaud this determination falls 

 short of the desired accuracy on account of the uncer- 

 tainty of the corrections for refraction. This is partly 

 due to the observations having all been made during 

 midsummer, but chiefly to the bad position of the 

 Observatory at the extreme south of Paris, the observa- 

 tions of Polaris therefore being made with the telescope 

 pointed over the entire breadth of the city. It is hoped 

 that the great Eiffel tower may render assistance to the 

 study of refraction by affording much information as to 

 inversions of the usual law of the variation of temperature 

 with the height. The above value for the latitude still 

 remains to be corrected for flexure of the instrument, and 

 M. Perigaud is now undertaking the study of this error. 

 The total number of meridian observations obtained 

 during the year was 16,318, the highest monthly number 

 having been secured in February, a most unusual circum- 

 stance. The observations of sun, moon, and planets 

 amounted to 545. 



The observations with the equatorials have been of the 

 usual kind. M. Bigourdan has made 400 measures of 

 nebulae with that of the West Tower ; and M. Obrecht, 

 with the equatorial coude', has made 720 measures of 

 lunar craters referred to different points of the limb, in 

 order to secure a better determination of the form of our 

 satellite. But a yet more important work with this latter 

 instrument has been the thorough examination of its 

 theory by MM. Lcewy and Puiseux. In view of the success 

 of the Paris telescope, of the number of similar instru- 

 ments now under construction, and of the still wider 

 popularity which the same form will probably have in 

 the future, this was a work much to be desired. 



The results, however, achieved in the field of astro- 

 nomical photography are those in which, in view of the 

 proposed chart, the greatest interest will be felt just 

 now, and here the MM. Henry have further evidences 

 of progress to present. Saturn and the moon have been 

 photographed with a direct enlargement of 20 diameters. 

 The phases of the lunar eclipse of August 3 have been 

 recorded by the same means. With the smaller photo- 

 graphic instrument, aperture 4"3 inches, negatives 

 have been obtained, one of which showed more than 

 30,000 stars on the single plate. Several curious new 

 nebulas have been discovered, one 1° in length near 

 C Orionis ; but the most remarkable have been those in 

 the Pleiades. Two plates of this group, each with an 

 exposure of four hours, have not only added much to our 

 knowledge of the nebulae round Electra, Merope, Maia, 

 and Alcyone, these no longer appearing as mere faint 

 clouds, but as well-marked nebulosities of intricate and 

 complicated forms, but two new nebulas are shown, both 

 very narrow and straight, the longer one being some 40' 

 in length and but 2" or 3" in breadth, and threading 

 together as it were no fewer than seven stars. The plate 

 representing this photograph of the Pleiades, which is 

 attached to the Report, shows 2326 stars, and comprises 

 stars of the 18th magnitude, instead of the 1421 stars 

 contained in the earlier photograph. MM. Henry have 



