March i6, 1876] 



NA TURE 



391 



up with sandstones, conglomerates, and breccias. The 

 red stain of these deposits, occasional pseudomorphs of 

 rock-salt and layers of gypsum, combined ^vith ripple- 

 marks and sun-cracks seem, as Prof. Ramsay has sug- 

 gested, to indicate the concentration of the saline waters 

 which filled these basins ; while further evidence of the 

 unwholesome nature of the water may be indicated by 

 the general paucity of fossils in the strata, and by the 

 immense numbers of well-preserved fishes which are 

 sometimes met with crowded into a small space, as if they 

 had come from fresher water elsewhere, and had been 

 inclosed and killed in scattered pools. The peculiar 

 breccias and brecciated conglomerates of the Upper Old 

 Red Sandstone have been compared to some recent 

 Glacial deposits, and the resemblance has been pointed 

 out between the form of the stones in these deposits, and 

 those in common boulder-clay. It should be noted also 

 that in many cases these breccias occur in old valleys, 

 and bear many of the characters of valley-moraines. 

 Such are those to the east of UUswater, and those which 

 flank, and in some places penetrate the Lammermuir 

 Hills. In the latter district worn dome-shaped bosses of 

 rock underlpng the breccias recall the aspect of true 

 roches moiitonnees. Another glacial feature is suggested 

 by the basin-shaped hollows (apparently sometimes true 

 rock-basins) in which the deposits lie. Further indica- 

 tions of ice are given by the remarkable patches of 

 angular and rounded stones scattered through the red 

 sandstones of Arran, the occurrence and position of which 

 may be accounted for on the supposition that they are 

 portions of shore- gravel, which have been frozen and 

 transported in cakes of floating-ice. 



Indications of terrestrial disturbance during the accu- 

 mulation of the Upper Old Red Sandstone in Scotland 

 are furnished by the Lammermuir Hills. Towards the 

 close of the period, and thence through the deposition of 

 the Lower Carboniferous rocks, volcanic action which 

 seems to have been quiescent for a long interval, broke 

 out again over the south of Scotland. To this period 

 belongs the chain of old lavas and tufi^s which may be 

 traced from the mouth of the Nith eastwards by Lang- 

 holm and the Tarras Water, to the head of the Slitrig 

 Valley, and through the plain of the Tweed as far north- 

 wards as the Whiteadder. The Garlton Hills, Campsie 

 Fells, and the ranges of hills which run down Renfrew- 

 shire and the north-east of Ayrshire, and are prolonged 

 into Bute, the Cumbrays and Arran mark a prolonged 

 series of volcanic eruptions during this same period. 

 Probably the terraced hills of Lome are of similar age. 

 Traces of contemporaneous volcanic action occur likewise 

 in the Upper Old Red Sandstone of the north of Scotland, 

 and form a remarkable feature in the cliffs of Hoy, one of 

 the Orkney Islands. 



The author brought forward evidence to show that 

 while the Upper Old Red Sandstone was being deposited 

 in the British area, there existed outside that area a sea in 

 which some of the characteristic corals, brachiopods, and 

 other organisms of the time of the Carboniferous Lime- 

 stone already existed. He pointed out the intercalation 

 of limestone bands in the Red Sandstone series in Arran 

 and elsewhere, a long way below the base of the Cement- 

 stone group which underlies the Carboniferous Lime- 

 stone. These calcareous bands, full of species of fossils 

 which are familiar in the Carboniferous Limestone, seem 

 to indicate that while, on the whole, the Upper Old Red 

 Sandstone, and the red strata at the base of the Carbon- 

 iferous system were deposited under conditions unfavour- 

 able to the presence of at least corals, crinoids, and 

 molluscs, their formation was interrupted by intervals 

 during which clearer and less saline water prevailed, 

 perhaps owing to the removal of barriers which allowed 

 the access of the main ocean with its animal forms into 

 the closed lagoons and inland seas of the Upper Old 

 Red Sandstone. 



ON REPULSION RESULTING FROM RADIA- 

 TION-^ 



'"PHIS paper contains an account of experiments on the 

 ■*• action of radiation on bodies the surfaces of which 

 have their radiating and absorbing powers modified by 

 various coatings. The difference between a white and a 

 lamp-blacked surface in this respect was at first not very 

 decided, and experiments have been instituted with the ob- 

 ject of clearing up some anomalies in the actions observed. 

 Two pith discs, one white and the other black, are suspended 

 on a light arm in a glass bulb by means of a fine silk 

 fibre ; after perfect exhaustion the white and black discs 

 are found to be equally repelled by heat of low intensity, 

 such as from the fingers, warm water, &c. A copper ball 

 is then tried at gradually increasing temperatures. Up 

 to 250° C. it repels bota equally, above that the black is 

 more repelled than the white, and at a full red heat the 

 repulsion of the black disc is very energetic. A lighted 

 candle acts with more energy than the red-hot copper. 



The presence of even a small quantity of aqueous 

 vapour in the exhausted apparatus almost, if not quite, 

 neutralises the more energetic action which luminous 

 rays appear to exert on a blackened surface. 



After describing several different modifications and 

 some new forms of apparatus devised to facilitate experi- 

 ment, the author gives a drawing of an instrument which 

 enables him to get quantitative measurements of the 

 amount of incident light falling on it. It consists of a 

 flat bar of pith, half black and half white, suspended hori- 

 zontally in a bulb by means of a long silk fibre. A small 

 magnet and reflecting mirror are fastened to the pith, 

 and a controlling maijnet is fastened outside so that it 

 can slide up and down the tube, and thus increase or 

 diminish sensitiveness. The whole is completely exhausted 

 and then inclosed in a box lined with black velvet, with 

 apertures for the rays of light- to pass in and out. A ray 

 of light reflected from the mirror to a graduated scale, 

 shows the movements of the pith bar. The degrees of 

 deflection produced by the light of a candle at distances 

 from 6 feet to 35 feet are given. 



The experimental observations and the numbers which 

 are required by the theoretical diminution of light with 

 the square of the distance, are sufficiently close, as the 

 following figures show : — 



o 



Candle 6 feet off gives a deflection of 218 



12 

 18 

 24 

 10 

 20 

 30 



54 

 24-5 



13 



n 



8-5 



The effect of two candles side by side is practically 

 double, and of three candles three times that of one 

 candle. 



The action of various solid and liquid screens is next 

 given, 



A candle three feet off, giving a deflection of 180'', has 

 its action reduced to the following amounts by 



Yellow glass . . . 

 Blue „ 

 Green „ 

 Red „ 

 Water „ 

 Alum 



i6i 

 102 



lOI 



128 



47 

 27 



A candle on each side of the apparatus, and equidistant 

 from it, keeps the index ray of light at zero ; by shading 

 off either one or the other the light flies off to either 

 extremity of the scale. This gives a ready means of 

 balancing two sources of light one against tne other. Thus, 



I Paper read at the Royal Society, Feb. lo, by William Crookes, F. R.S., 

 &a Part III. 



