to account for the observed phenomena ina satisfactory manner. 
As is required by this theory it is found that the addition of 
neutral acetates toa solution of acetic acid diminishes the anti- 
septic power of the acid, the concentration of the active com- 
ponent of the solution, the hydrogen ion, being under these 
circumstances reduced to a much smaller value. 
Numerous theories have been put forward at different times 
to account for the formation of natural paraffins, the one re- 
ceived with most favour being that due to Berthelot and de- 
veloped by Mendeléeff in which the action of steam upon 
metallic carbides was regarded as the main source of the hydro- 
carbons. The chief stumbling block to this view was the diffi- 
culty of explaining the mode of formation of the naphthenes of 
the Russian oilfields. The researches of MM. Paul Sabatier and 
J. B. Senderens on the action of reduced nickel, iron and other 
metals upon hydrocarbons have now placed the ‘‘ chemical ” 
theory of petroleum formation on a firm experimental basis. By 
the direct hydrogenation of acetylene in the presence of nickel 
they have obtained liquid mixtures of hydrocarbons which can 
be made to correspond either with American or Caucasian 
petroleum by varying the conditions of the experiment. To 
account for the formation of petroleum it is thus sufficient to 
admit that there are in the depths of the earth free alkali metals 
and metallic carbides, which in contact ‘with water give rise to 
mixtures of hydrogen and hydrocarbons. These gases encounter 
nickel, cobalt or iron in a finely divided state, and thus give 
rise to the mixtures of hydrocarbons forming natural 
petroleum. 
THE additions to the Zoological Society’s Gardens during the 
past week include a Bosman’s Potto (Perodécticus potto) from 
West Africa, presented by Mr. Edward Straw ; three American 
Bisons (42son americanus) from North America, presented by 
H.G. the Duke of Bedford, K.G., P.Z.S.; three Darwin’s 
Rheas (&hea darwin) from Patagonia, a Red Ground Dove 
(Geotrygon montana) from South America, presented by Capt. 
John L. Marx, R.N. ; two Garden’s Night Herons (Vyctzcorax 
gardent) from the Falkland Islands, presented by Mr. W. Grey 
Wilson, C.M.G, ; an Algerian Tortoise (7Zestudo ibera) from 
North Africa, presented by Master C. Treverlyn Gill; a Silvery 
Gibbon (Hy/obates leuctscus) from Java, deposited ; six Ruddy 
Flamingoes ( Phoentcopterus ruber) from North America, twenty 
Alpine Newts (d/olge alfestris), twenty Newts (JZolge 
montandonit) from Roumania, purchased ; a Thar (Hemetragus 
semiaica) born in the Gardens. 
THE EQUATORIAL CURRENT ON JUPITER. 
yt differences occurred in the rate of motion of different 
markings on Jupiter was first discovered by Cassini in the 
seventeenth century. But other observers in later years appear 
to have neglected the systematic study of the planet. His disc 
was occasionally surveyed, it is true, and the positions of the 
belts described, but the details were not perseveringly followed. 
Telescopes were formerly of inordinate length and not very 
effective in performance, but what was accomplished by Cassini 
might also have been achieved by others. Jupiter’s dimensions 
are such that comparatively small and imperfect instruments 
are capable of revealing the principal markings. Herschel never 
made a thorough investigation of the Jovian spots, though he 
obtained some observations in 1779 and recognised the difference 
in their motions. Until the last half of the nineteenth century 
the planet seems to have been generally surveyed ina desultory 
manner. 
The apparition of the great red spot, however, revolutionised 
the existing state of things, for it was destined, not only to attract 
an immense amount of attention to itself, but to the whole visible 
phenomena presented by the surface markings of Jupiter. When 
this remarkable object first became perceptible it is not our 
purpose to inquire ; it is certain, however, that as an exception- 
NO. 1701, VOL. 66] 
NATURE 
[JUNE 5, 1902 
ally conspicuous feature it was widely observed during the last 
half of 1878. 
It was long thought that the equatorial region of the planet 
supplied us with the most swiftly moving objects. This was, 
however, found to be a mistaken impression. The white and 
dark equatorial spots completed a rotation in about 54 minutes 
less time than the red spot, and this meant a difference of 
velocity amounting to about 250 miles per hour. But it was 
soon seen that though the equatorial current is much more rapid 
than the rate exhibited in certain other latitudes, it does not 
equal the velocity of some other occasional markings in the 
northern hemisphere. 
It is only our intention, however, to refer briefly to the equa- 
torial markings observed during the last quarter of a century. 
But it must be confessed that the observations are not nearly 
so continuous and complete as the importance of the subject 
demands. The results have been sufficiently full forall purposes 
during the last few years, for several observers, including Mr. 
A. S. Williams, Rev. T. E. R. Phillips, Captain P. B. Moles- 
worth and others, have obtained a mass of useful materials with 
reference to the equatorial current. And there seems no doubt 
that the investigation will be adequately maintained. It is 
chiefly to the continuity of the observations that we must look 
for the satisfactory elucidation of the phenomena presented. 
The equatorial spots have not, it is true, been always in strong 
evidence. In certain years they are liable to be almost, if not 
entirely, absent. The breaks, therefore, which occur amongst 
the accumulated observations are not always to be ascribed to 
negligence on the part of Jovian students. 
At present the equatorial spots are both numerous and con- 
spicucus, and it is to be hoped that a large addition to our 
observations will be effected during this opposition. The results 
for preceding years are very extensive and exhibit an irregular, 
though on the whole a decided, increase in the rotation period, 
but it would be premature to undertake the collection and re- 
duction of all the materials. The observations must be pro- 
longed over a much more lengthy interval before they can be 
expected to reveal the information we require. As observed at 
Bristol, the equatorial spots have shown the following variations 
in their rotation period, but satisfactory mean results from a 
number of different objects were only obtained during the last 
four oppositions :— 
hh, iraeess 
1880 950 5°8 I very bright spot 
1881 950 88 55 x, 
1882 9 50 114 » 23 
1883 9 50 I2°I » = 
1885 9 50 14°3 23 93 
1886 9 50 22°8 io on 
1895 9 50 34°3 2 black spots 
1898 9 50 23°6 23 spots 
1899 9 50 24°6 275 
1900 9 5C 24°1 18 ,,; 
1901 Q 50) 2951s .eet) ZONIs5 
W. F. DENNING. 
GERMAN PROGRESS IN OPTICAL WORK.' 
il PURPOSE dealing with statistics compiled from information 
afforded me by two German firms and one Austrian, Messrs. 
Zeiss, Leitz and Reichert respectively, all of whom are well- 
known makers of microscopes, and the first named of many 
other optical instruments, including prismatic field glasses, of 
which, as is well known to you all, they were the originators. 
I must say that the figures quoted refer approximately to the 
end of the year 1899, since which date the average rate of 
increase has been more than maintained. Taking first the firm 
of Zeiss, in Jena, twenty years ago they employed fifty men ; 
five years later the number had leaped up to 170, or more than 
three times as many ; in another five years the number had prac- 
tically been doubled, 327 being the precise number ; yet another 
five years saw the number 580 ; while to-day (1899) they employ 
the astonishing number (astonishing, that is, for the class of in- 
struments they manufacture) of 946 men, this grand total being 
made up as follows: theoretical staff, 22 ; office and dispatch, 
36; mechanics, 322 ; opticians, 371 ; wood-workers, leather- 
1 Abridged report of a paper entitled “‘ The Secret of German Progress,” 
read before the Optical Society by Mr. Herbert F. Angus, Hon. Sec. of the 
Educational Committee of the Society. 
ee 
