l82 



NA TURE 



[June 19, 1890 



stream of chlorine slowly allowed to pass through it. The very 

 volatile methylene chloride distils over, as it is formed, into a 

 condenser which is strongly cooled by a freezing mixture. In 

 order to prepare the new gas, the methylene chloride is placed 

 in a tube of Bohemian glass along with the proper quantity of 

 pure silver fluoride, and the tube sealed before the blow- 

 pipe. It is then heated for half an hour to i8o°. In 

 an actual experiment l"7 gram of methylene chloride and 5'o8 

 grams of anhydrous silver fluoride, specially purified by the 

 method described by Gore, were employed. Upon opening 

 the tube, a great rush of gas occurs, which on collection and 

 analysis is found to consist of methylene fluoride. The density 

 of the gas compared with air was found to be i'82, which 

 agrees very closely with the theoretical density, i"8i, required 

 for the formula CHgFg. Alcoholic potash is found to absorb it 

 completely. Hence, in order to obtain a measure of the amount 

 of carbon contained in the gas, a measured volume was absorbed 

 in alcoholic potash and then treated with acetic acid and 

 potassium permanganate. The alcoholic potash appears to con- 

 H, 



vert it into formaldehyde, 



v 



H^ 



potassium permanganate to carbonic acid. 



this is oxidized by the 

 HOx 



HO 



/' 



o, and the 



acetic acid consequently liberates a volume of carbon dioxide 

 equal to the volurrie of methylene fluoride experimented upon. 

 This affords a ready mode of demonstrating at the same time 

 the principal properties of the gas and its composition as regards 

 the amount of carbon contained in it. Experiments are now in 

 progress from which it is hoped some knowledge will be gained 

 concerning its physiological action, which it will be interesting 

 to compare with that described by MM. Regnault and Villejean 

 in case of methylene chloride. In a recent communication by 

 M. Moissan upon carbon tetrafluoride, CF4, an account of which 

 Vi'as given in Nature (May 15, p. 67), it was recommended that 

 metallic tubes should always be employed in these reactions with 

 silver fluoride, inasmuch as fluorides of carbon attack glass with 

 production of carbon dioxide and silicon tetrafluoride ; for in- 

 stance, CF4 + SiOj = CO2 + SiF^. But M. Chabrie finds that 

 if hard Bohemian glass is used, the product contains only mere 

 traces of the two gaseous impurities mentioned, and, as glass is 

 so much more convenient to manipulate, considei-s it advisable 

 to use it. The methylene fluoride prepared in the above manner 

 was quite sufficiently pure for all practical purposes. 



The additions to the Zoological Society's Gardens during the 

 past week include a Common Marmoset {Hapale JaccJms) from 

 South-east Brazil, presented by Mr. Percy Standish ; a Mal- 

 brouck Monkey [Cercopithecns cynosurm i) from the Upper 

 Shire, two Grand Galagos {Galago crassicaudata) from Mandala, 

 Shire Highland, East Africa, presented by Mr. John W. Moir ; 

 two Common Marmosets {Hapale jacchus) from South-east 

 Brazil, presented by Mr. W. Norbury ; a Common Fox {Canis 

 vulpes i), British, presented by Mr, Atkins; a Great Crested 

 Grebe {Podiceps crisialus), British, presented by Mr, T. E. 

 Gunn ; two Green Lizards {Lacerta viridis), three Wall 

 Lizards {Lacerta inuralis), a Dark-Green Snake {Zamenis atro- 

 virens), four Common Snakes [Tropidonotus natrix), four 

 Marbled Newts {Molge marmorata), an Edible Frog {Rana 

 esculentd) from the South of France, presented by the Rev. 

 F, W, Haines ; eighteen Young Green Turtles ( Cheione viridis) 

 from Ascension Island, presented by Captain Robinson ; a 

 Silvery Gibbon {Hylobates letuisciis) from Java, deposited ; a 

 Philippine Paradoxure {Paradoxurus philippensis) from Zebu 

 Island, Philippines, three Japanese Teal {Querquedula formosa 



(S 9 ? ) from North-east Asia, purchased ; an Angora Goat 

 {Capra hircus, var., $), two Yellow-legged Herring Gulls 



{Lartts cachinnans) bred in the Gardens. 

 NO. 1077, VOL. 42] 



OUR ASTRONOMICAL COLUMN. 

 Objects for the Spectro'scope. 

 Sidereal Time at Greenwich at 10 p,m, on June 19 = 

 iSh. S2m, i8s. 



Remarks. 

 (i) The spectrum of this nebula, according to an observatior> 

 made by Dr. Huggins in 1866, is a continuous one, but this 

 result does not appear to accord with Smyth's description of it 

 as "a fine planetary nebula, . . . large, round, and of a lucid 

 pale blue hue." The G,C, description of it is : "Very bright , 

 large ; round ; disk with faint, possibly resolvable, border," I 

 know of no later observation of the spectrum than that referred 

 to, but it is important that it should be confirmed, as the colour 

 alone would lead to the supposition that there is something in 

 addition to continuous spectrum. It is indeed possible that we 

 have here a case of a nebula intermediate in condensation 

 between those which give a spectrum of bright lines, and 

 those which give a so-called "continuous" spectrum. In any 

 case the apparent discrepancy between colour and spectrum 

 should be investigated, for it is generally understood that planet- 

 ary nebulae with a bluish colour give bright lines, 



(2) Duner describes the spectrum of this star as a magnificent 

 one of Group II. "All the bands 2-10, 6 included, and possibly 

 I, are visible. They are of extraordinary width and entirely 

 black. The spectrum is totally discontinuous," The usual 

 more detailed observations should be made. 



(3) This star has a spectrum generally described as similar to 

 the solar spectrum. The usual more detailed observations, as 

 to whether the star is increasing or decreasing in temperature, 

 are required. 



(4) The spectrum of this star is a well-marked one of Group 

 IV., but so far we have no information as to the temperature of 

 the star relatively to others with almost similar spectra. 



(5) The spectrum of this variable has not been recorded.^ 

 The range of variation is from 8 '5 to 14 in about 260 days. 

 There will be a maximum about June 20. A, Fowler. 



Observations of Meteors. — The May number of the 

 Monthly Notices of the Royal Astronomical Society contains a 

 catalogue of 918 radiant-points of meteors observed by Mr, 

 Denning at Bristol since 1873, together with a mass of informa- 

 tion pertaining to their determination. The total number of 

 meteors seen from 1873 to 1889 was 12,083, and the paths of 

 9177 of these were registered. The following table shows the 

 horary rate of apparition of the meteors during the various- 

 months of the year : — 



January ... 65 July ii*3 



February ... 4*9 August 11 '3 



March 6 6 September ... 10-3 



April 6-6 October 11 "8 



May 5-2 November ... 11*3 



June 4"9 December ... 8'9 



The mean horary rate of apparition is therefore 8*3. This is- 

 less than would be observed from a place where there is no 

 interference with the light and smoke of a large town, some 

 observations made by Mr. Denning in a different locality in- 

 creasing the mean horary number to il '4. 



The observations were almost equally distributed between the 

 morning hours, and were usually made between the third and 

 first quarter of the moon, because a bright sky is veiy effective in 

 obliterating meteor-showers, and therefore moonlight meteors 

 are commonly rare. 



As to the relative numbers which appear during the night, 

 the maximum appears to be attained between 2 and 3 a.m., 

 when the rate is nearly double that observed in the early hours- 

 of the evening. Two or three meteors have frequently been 

 noticed to appear at nearly the same time and from the same 

 radiant, the probable explanation in such cases being that the 



