20 



NATURE 



[May 



optical parts, Prof. Vogel says : " The objectives are very 

 beautiful and colourless ; the prisms are masterpieces of work- 

 manship ; the glass of which they are composed is pure, colour- 

 less and free from streaks, and only in two prisms do a few air 

 bubbles appear." The spectra given by the prisms are said by 

 Prof. Vogel to be very excellent, and the working of the whole 

 set of prisms exceeds even to-day any other instrument of the 

 same dispersion. The refractive angles of the piisms, as 

 measured by Dr. Ilartmann, are 44° 57''i, 45° 6'"9, 45° 26''9 

 and 59° 50' 8, and the relative refractive indices at a temperature 

 of 18° C. was found by the same observer to be for the lines — 



Iupiter's Red Spot. — Jupiter is now in a good position for 

 observation, and his surface markings have become of late of 

 great interest in. consequence of the numerous spots which many 

 observers have seen on his disc. Dr. A. A. Nijland draws 

 attention to two very curious spots {Astr. Nachr., No. 3488) 

 which are situated on the northern hemisphere, their coordinates 

 in longitude and latitude (according to " Marth's System," ii., 

 Monthly Notices, Iviii. p. 107) being A = 272° fi + 31°, 

 A = 289° 3 = + 38°. Dr. Fauth, from the private observatory 

 at Landstuhl, gives us a continuation of the list of longitudes of 

 several prominent spots observed by him. Another short com- 

 munication of interest is that which appears in the Astr. Nach., 

 No. 3490. In this Dr. Lohse discusses the movement of the 

 great red spot from observations extending over a period of twenty 

 years. The proper motion of the spot is, according to him, dis- 

 tinct and regular, and this will be clearly -seen from the short 

 table given below. 



The method of reducing this proper motion was to obtain for 

 each opposition a normal position for the centre of the spot on 

 the surface of Jupiter, on the assumption of a fixed meridian and 

 a regular velocity of rotation of the planet. In plotting the 

 positions of these deduced normal positions on paper with the 

 time as abscissce and the Jovian longitudes as ordinates, a regular 

 and symmetrical curve was brought to light. The following 

 figures give the Jovian normal longitudes of this spot as shown 

 in this manner, together with the name of the observer : — 



PETROLIFEROUS SANDS AND MUD 

 VOLCANOES IN BURMA. 

 'T'HE occurrence of petroleum in Burma, and its technical ex- 

 ■*• ploitation have, in a recently published volume, been very 

 fully treated by Dr. Fritz Noetling, paleontologist to the Geo- 

 logical Survey of India (Mem. Geol. .Survey India, vol. xxvii. 

 part 2). The Yenangyaung oil-fields occupy an area of about 

 350 acres on the borders of the left bank of the Irawadi, a few 

 miles distant from the river. They have been known from time 

 immemorial, while the methods of obtaining the oil at the 

 present day differ but little from those of a hundred years ago. 

 In 1855 there were about 130 productive wells ; there are now 

 about 600, together with six or seven bore-holes. The oil-field 

 is situated in a low but rugged table-land which is intersected 

 by numerous ravines, and the strata which yield the oil have 

 been bent into a gentle dome-like anticline. "The strata consist 

 of sands or soft sandstones, and shales of Tertiary ages overlaid 

 by drift. The oil is held in the sandy beds, the thickest of 

 which (though not the richest in oil) is a little over 130 feet. As 

 many as ten bands yielding oil may occur in vertical succession ; 

 but water and petroleum occur independently in different beds, 

 or in the same layer, and in the latter cise the petroleum 

 generally rests on the water. 



Oil has been found by boring in a bed of sandstone 900 to 

 1000 feet deep, but the main oil-sand is from 200 to 350 feet 

 from the surface. The sands are somewhat inconstant in 

 character, and the strata generally exhibit false-bedding. They 

 have yielded numerous remains of land mammalia and reptiles, 

 as well as some marine fossils, so that Dr. Noetling be- 

 lieves the strata were accumulated in shallow water not far from 

 land, and that carcases of animals brought do-.vn by a river were 

 entombed in the estuarine sediment. He regards the petroleum 

 as indigenous in these sandy estuarine or deltaic deposits. The 

 clays contain no trace of it. Moreover, he considers that the 

 strata were laid down on a plane gently inclined towards the 

 sea, and that this inclination facilitated a sliding of the .sediments 

 seawards, whereby certain minor folds and irregularities, other- 

 wise difficult to explain, were produced. These folds were inter- 

 sected by cracks, which became filled with mud— like veins of 

 eruptive material. 



Turning his attention to the mud volcanoes of Minbu, Dr. 

 Noetling points out that they are connected with sul>terranean 

 petroliferous strata : both volcanoes and mud-wells produce a 



The Mud Volcanoes of Minbu, in Burma (Dr. F. Noetling). 



The observers mentioned above were Loh.se, Trouvelot, Stanley 

 ■Williams, Denning, Terby, and Pritchett. From the curve it can 

 be seenjat a glance that the spot in the year 1891 rotated in the 

 same time as that assumed for the rotation of the planet. The 

 curve at this period has reached a turning point, and the longi- 

 tudes of the spot commence now to increase instead of decrease. 

 The observations show that for thirteen years (1878-1891) this 

 spot has moved through nearly three-quarters of the whole 

 circumference of the planet, and since that interval has begun 

 to retrace its path. The fact of such a distinct acceleration 

 and retardation of the motion of this large spot will, if the 

 observations be continued, help us probably to gain some 

 knowledge of the system of circulation involved in the Jovian 

 atmosphere. It would be interesting to know whether any 

 other comparatively large marking on the planet's surface follows 

 the same or a similar law. 



NO. 1488, VOL. 58] 



greyish-blue mud more or less saturated with petroleum. The low 

 temperature of the ejected mud, seldom so much as 85°, indicates 

 that its source is not deep-seated. Some of these mud volcanoes 

 are figured (the accompanying illustration is reduced from a Plate 

 in the Memoir. ) The largest had, in 1888, a crater about 6 feet in 

 diameter, and this was filled with viscous mud from which rose 

 enormous bubbles of inflammable gas with a strong odour of 

 petroleum. The temperature was 76°. Some of the other cones 

 rise about 30 feet from the ground. Jt seems at first difficult to 

 .say why mud volcanoes occur at Minbu and not at Yenangyaung, 

 but Dr. Noetling points out that at Minbu these volcanoes arise 

 through fis-sures in the Tertiary strata beneath an alluvial cover, 

 and he considers that the pressure of gas and petroleum forced a 

 way through this comparatively thin overlying deposit. No fiery 

 eruptions have been recorded ; in fact, there are no known in- 

 stances of spontaneous combustion. 



Dr. Noetling traces some connection between the fluctuating 

 heights of the river and the production of petroleum at the wells. 



