464 



NATURE 



[June 9, 192 1 



rocks at Bardal were under the sea before Allee 

 Couverte times. There may have been a 

 cultural survival from the Maglemose civilisa- 

 tion, even if they are Late Neolithic in age. 

 Is it possible that the new and interesting- 

 find of an engraved animal on a piece of crust 

 at Grime's Graves is to be correlated with this 

 group ? 



Group 5. Bronze-age rock carvings of South 

 Scandinavia, with an outlier in North Russia. 

 This group, which is especially concentrated in 

 Bohuslain (north of Goteborg), is too well known 

 to be discussed here further. It is dated from a 

 consideration of the form of daggers figured, as 

 well as from the carved ornamentation. Runes 



are never found in association with these rock 

 carvings. 



The North Russian outlier is of some in- 

 terest, and will be partly described this year. 

 The carvings are found here on extremely 

 hard, glacier-worn surfaces of rock, forming 

 the eastern shore of Lake Onega, south of 

 Pudosh, and north of the Black River. There 

 are ships, swans, a devil lo ft. long, animals, 

 a phallic scene, fish, signs, etc. (Figs. 3 and 4). 



Group 6. Maritime Alps. This group is also too 

 well known to require further discussion. The 

 occurrence of a ploughing scene, very similar to 

 one found in the Bronze-age group of South Scan- 

 dinavia, may be noted. 



Dark Nebulae. 

 By Dr. A. C. D. Crommelin. 



SEVERAL years ago photographs taken by 

 Profs. E. E. Barnard and Max Wolf ren- 

 dered the hypothesis highly probable that many 

 of the dark lanes and spaces met with in the 

 Galaxy and in regions of diffused nebulosity were 

 due to the intervention of occulting matter rather 

 than to actual diversity of star distribution. One 

 of the most notable examples occurs in a long 

 strip of nebulosity that runs southward from 



Fig. I. — Nebulosity south of f Orionis. From a 

 photograph taken by Mr. Duncan with the loo-in. 

 telescope of the Mouot Wilson Observatory. 



t, Orionis. Dr. Isaac Roberts noted that there was 

 "an embayment, free from nebulosity, dividing it 

 into halves." Prof. Barnard afterwards remarked 

 that this space appeared to be " a dark body, pro- 

 jected against, and breaking the continuity of, the 

 brighter nebulosity." More recently still the object 

 has been photographed at the Lick and Mount 

 Wilson observatories. The Mount Wilson photo- 

 graph, taken with the lOo-in. Hooker telescope, is 



NO. 2693, VOL. 107] 



here reproduced, and' is quite startling from the 

 hard, clear-cut outlines of the marking, which is 

 blacker than the neighbouring sky background. It 

 would seem that this sharp outline must indicate a 

 stratum of dust rather than one of gas ; it can be 

 I traced for some distance outside the long nebula, 

 and is probably connected with an isolated bright 

 nebula some 15 minutes of arc distant to the north- 

 east. It will be remembered that a great part of 

 Orion is covered with faint nebulosity, first re- 

 vealed as a large spiral by Prof. Barnard's photo- 



FiG. 2. — Enlargement of dark nebulosity in Fig. I. 



graphs with a lantern lens. There is a striking 

 falling off of star-density to the east of the long 

 ^ Orionis nebula as compared with that to the 

 west, which presumably indicates a general 

 absorption of light. 



The Proceedings of the Amsterdam Academy of 

 Science, vol. xxiii.. No. 5, contains two papers by 

 Dr. A. Pannekoek on a region of dark nebulosify 

 in Taurus. Dr. Pannekoek refers to a paper by 

 Sir F. W. Dyson and P. J. Melotte (M.N.R.A.S., 

 vol. Ixxx., p. 3). He uses their figures of star- 

 density in these regions to make an estimate of 



