Feb. 2 1, 187SJ 



NA TURE 



323 



taining a column of mercury, the rising and falling of which 

 under influences of barometric pressure raised or lowered the 

 centre of gravity of the pendulum and varied the rate of the 

 clock accordingly. The clock-train in both instruments was so 

 arranged that the dial-readings could, by an exceedingly simple 

 calculation, be interpreted in terms of mean daily thermo- 

 mctrical or barometricalj variations. As the alteration in the 

 lengths of the pendulums takes place second by second through- 

 out the day, it follows that the daily error of time shown on the 

 dial must be proportional to the mean of the variations of the 

 thermometer or barometer during the same period. 



The method of estimating, by observation of the rate of an uncom- 

 pensated time-keeper, the mean amount of heat received during 

 any given period, without the necessity of recording the actual 

 temperature at any particular time, is not by any means new, for 

 the chronometrical thermometer, an instrument which has for 

 many years been emplijyed at the Royal Observatory for testing 

 the rates of chronometers under variations of temperature, is 

 founded upon the same principle. This instrument consists of a 

 chronometer in which the usual compensation for temperature is 

 reversed ; that is to say, in the balance the positions of the brass 

 and the steel are interchanged, the latter being outside, so that 

 variations of temperature produce an exaggerated effect upon 

 the rate of the instrument, 



M. von Stemeck is probably the fiist to su^^gest the employ- 

 ment of the chronometrical method to the determination of mean 

 variations in the vertical intensity of terrestrial magnetism, but 

 he has, I think, been anticipated in its application to the com- 

 puting of thermometric and barometric averages. 



Scie^itific Club, February 18 Conrad W. Cooke 



BACTERIA IN WATER 



IT is well known that water — whether tap or ordi- 

 nary distilled — possesses the property of contami- 

 nating, with a growth of bacteria, any " cultivation " 

 liquid inoculated with it, but the morphological con- 

 dition in which these organisms occur in it is open to 

 question ; it may be supposed on the one hand, that they 

 exist as developed bacteria, and are not apparent under 

 the microscope merely in consequence of their scarcity, as 

 shown by Mr. Lister in the account of his recent admir- 

 able investigation of the lactic fermentation, to be the 

 case with some specific ferments, or, on the other hand, 

 that they are present as " germs " of the bacteria, bodies 

 yet far more minute than the mature forms, and on that 

 account invisible — ultra-microscopic. Which of these 

 alternatives is true I have endeavoured to determine by 

 experiment, the details of which will shortly be published, 

 and the general result is here briefly communicated. 



M. Pasteur has recently stated in the Comptes Bcndiis, 

 that if a cylinder of water be allowed to stand for several 

 weeks at a constant temperature, the organisms in it sink 

 to the bottom, leaving the upper portion free, and incapable 

 of contaminating. Following this method and placing a 

 vessel of ordinary distilled water in an apparatus con- 

 structed for the purpose of maintaining an invariable 

 temperature, after seven or eight days a specimen of the 

 water was taken from the bottom of the vessel by 

 a pipette closed with the finger and dipped into 

 it. The water so taken was in appearance perfectly 

 bright and pellucid, but under the microscope it was 

 found to contain amorphous particles, some spores of fila- 

 mentous fungi, micrococci in great numbers, bacteria of 

 the common form {B. Termo) and bacilli (long and 

 extremely slender filaments). All of these forms were 

 motionless, or exhibited only Brownian movement. No 

 such forms could be detected in the upper layers of the 

 water, nor in a specimen taken from the bulk of that 

 from which the experiments were made. As regards 

 limpidity, there was no difference between the top and 

 bottom portions. 



I have made four experiments with specimens of water 

 obtained from two different sources, and in all I have 

 been able by this method of subsidence to prove the 

 presence of organisms in great numbers in the sediment. 

 It may be me^ationed that they stain with facility by 



Hacmatoxylon, and are thereby rendered more readily 

 apparent. 



These observations show that bacteria occur in water 

 under their usual forms, and that they are not generally 

 distinguished on account of their small number, in any 

 one portion of the water, when disseminated through its 

 mass. The observed contaminating property of distilled 

 water is thus accounted for without necessitating the 

 assumption of " germs " of any sort, an hypothesis which 

 is unsupported by observation. 



The examination, by cultivation, of the difference in 

 contaminating properties of the upper and lower layers, 

 stated by M. Pasteur to exist, has as yet been inconclusive. 



G. F. DOWDESWELL 



OUR ASTRONOMICAL COLUMN 

 The Uranian Satellites, Ariel and Umbriel.— 

 The following positions of the two interior satellites of 

 Uranus for the ensuing fortnight are derived from the 

 data furnished by Mr. Marth in the January number of 

 the Monthly Notices of the Royal Astronomical So- 

 ciety, and are for iih. G.M.T,, or about the time of the 

 planet's meridian transit. There must be many telescopes 

 in this country which will command the two exterior 

 satellites, Titania and Oberon, but, so far as we know, 

 neither Ariel nor Umbriel have yet been certainly ob- 

 served here with any but Mr. Lassell's reflectors. Prof. 

 Newcomb states that Ariel is intrinsically brighter than 

 Umbriel ; he thinks that Ariel at least belongs to that 

 class of satellites of which the brilliancy is variable, and 

 dependent on its position in its orbit, and he adds that 

 the evidence of variability of some kind seems indisput- 

 able, since he has repeatedly failed to see it with the 

 Washington refractor when the circumstances — distance 

 from the primary not excepted — were favourable, and 

 when the next satellite, Umbriel, though less favourably 

 situated, was visible. " On the other hand," he remarks, 

 "there were two occasions, 1874, January 28, and 1875, 

 March 25, when it was surprisingly conspicuous," and at 

 these times the angle of position was about 350°. Prof. 

 Newcomb further expresses the opinion that where any 

 difficulty is experienced in seeing the outer satellites, he 

 would not hesitate to pronounce it impossible to see the 

 inner ones. 



Nevertheless, the success which has attended the search 

 for one, at least, of the satellites of Mars by English 

 observers who are provided with large instruments, may 

 perhaps induce them to look for the close satellites of 

 Uranus at the present opposition. 



Pigott's Observations of Variable Stars.— Some 

 years since it was suggested, we believe, by Prof. 

 Argelander, that the Royal Society might have in its 

 possession manuscripts of Edward Pigott of York, 

 amongst which might be found observations of variable 

 stars that would prove of importance in the history of 

 their fluctuations. It would appear, however, that none 

 of Pigott's papers are preserved in the Society's Archives, 

 an ineffectual search having been lately niade fpr them. 



