144 



NA TURE 



[Dec. ii, 1879 



greatest elongation 44 minutes before the place as computed : its 

 period as now ascertained is 7I1 . 39m. I3'996 sec. 



A paper by Prof. Joseph Le Conte on the old river-beds of 

 California, was read in the absence of its author, and attracted 

 much attention. These river-beds are now in process of being 

 washed out by hydraulic mining, in the search for gold ; and it 

 is in them that some of the earliest traces of prehistoric man are 

 alleged to have been discovered. Prof. Le Conte does not 

 regard the hydraulic method of attack as promising to yield 

 many fossils in good preservation ; it is more likely to destroy all 

 traces. The mode of formation of the old river-beds, which are 

 found in Middle California, is peculiar. Their rivers had been 

 completely displaced and have formed new channels, sometimes 

 parallel, and sometimes even at right angles to the old ones. The 

 new channels are cut perpendicularly through 2,000 to 3,000 feet 

 of slate rock. The old channels are filled with boulders and 

 pebbles ; capped with a conglomerate layer, described as " tri- 

 faceous," the product of a volcanic overflow, with few pebbles. 

 Under ordinary circumstances the tendency of rivers to clear their 

 own channels is effective, though sometimes operating at long in- 

 tervals. If the load of detritus is too heavy, it is deposited ; but 

 eventually there comes a time when the river is no longer over- 

 loaded, and then it proceeds to tear up and remove its previous 

 deposits. Thus at the present time the Colorado River is under- 

 loaded, and is cutting its channel, while the Platte is overloaded 

 and filling up; the Yuba River has filled a depth of 15 feet 

 within the past 20 years. But in the old river-beds under 

 consideration, the deposit has been capped and protected by a 

 volcanic overflow. We find evidences of this lava flood over a 

 vast district, but not extending to the British possessions. Prof. 

 Le Conte is inclined to fix the period of the lava flow as at the 

 boundary between the tertiary and quaternary. Whitney and other 

 geologists have referred the gravel of these river-beds to the 

 pliocene; Prof. Le Conte thinks that the fossils indicate the 

 approach of a change to the quaternary, and that the passage 

 from the pliocene to the glacial epoch was gradual. To review 

 the whole procedure, he begins with the elevation of the Sierras, 

 when a general drainage system was constituted without much 

 tendency to erosion. Glaciers formed and were melted, and thus 

 were provided the boulders and gravel. Then came the lava 

 flow, which destroyed the old drainage system, and compelled the 

 rivers to seek new channels. The further elevation of the 

 Sierras had renewed the glacial operations, which in some 

 instances had wholly swept away the lava and replaced it by a 

 different class of deposits. The paper elicited a very lively dis- 

 cussion, in which all the geologists present took part. Prof. 

 O. C. Marsh is inclined to give full weight to the views of Prof. 

 Whitney and Clarence King, who have been long in the field and 

 have studied the subject very thoroughly. Prof. Marsh said that 

 he himself has picked out fossil remains from these river-beds, 

 which were unquestionably pliocene, and of animals living in a 

 tropical climate. The volcanic outbreak certainly took place in 

 the pliocene, and before the glacial epoch ; of this he had 

 assured himself by observing the position of layers of basalt. 

 We find the remains of man in this position — in the pliocene, 

 along with remains of sloths and other tropical animals. We 

 concede that these animals were there in that era. Why must 

 we suppose that the remains of man were brought thither by 

 some accident? It seems more reasonable to believe that man 

 was there in that warm climate, in which he could live, than that 

 he came in with the cold and the glacial era. 



" Our Memory for Colour and Luminosity," was the subject of 

 an essay by Prof. O. N. Rood. He proposed to give a few 

 results from a series of experiments recently begun and not yet 

 completed. It is generally supposed that while we have a distinct 

 memory of different colours, such, for instance, as those which 

 are called "primary," we do not remember with definiteness, 

 particular shades of colour or specific mixtures of white and 

 black. Nearly all optical instruments in which there is a provi- 

 sion for comparing either colours or amounts of luminosity, are 

 constructed with great care so as to bring as nearly as possible into 

 contact the colours or shades to be compared. The prevailing 

 notion seems to be that we do not retain for ten seconds an exact 

 memory of a given shade or tint. Prof. Rood exhibited the 

 apparatus by means of which he tested the correctness of this 

 notion. Two disks were so arranged that either one could over- 

 lap the other in any required proportion. The disks were of 

 different colours, which blended into a given tint when the disks 

 were rapidly revolved — a tint having a known percentage of each 

 of its components. Let us suppose that this tint was obtained 



by thus blending 43 parts of yellow with 57 parts of red. Prof - 

 Rood wished to ascertain how near to that proportion he would 

 get when he reproduced that tint from memory. So he took a 

 glance at it while the disks were revolving. An assistant then 

 disarranged the disks, and afterwards proceeded to rearrange 

 them, making the blended tint more or less yellow as directed by 

 Prof. Rood, until the colour attained corre-ponded to the latter's 

 recollection of the original tint. The original having 43 per 

 cent, of yellow, the reproduced colour had — on an average of 

 many trials — 42-6 per cent, of yellow. This was when only a 

 minute elapsed between looking at the tint and reproducing it. 

 The largest variations from the mean were not over J of one 

 per cent., a difference of tint so slight as to be just barely per- 

 ceptible when it is shown by direct contrast and the superposition 

 of the differing shades. When an hour was allowed to elapse 

 before the colour was reproduced from memory, the tint obtained 

 averaged 45 2 of yellow, showing an error of 2"2 per cent, error. 

 Reproductions 24 hours afterwards gave 47'5 ; Le. 4J per cent. 

 Equally near results followed in testing the memory for other 

 mixtures of colours, such as yellow with green, and blue with 

 green. The amount of error in several of these instances was 

 exhibited to the Academy by means of the apparatus, and was 

 scarcely distinguishable. This power of memory for colours 

 might, however, be peculiar to this experimenter : to test that 

 point, a similar set of observations were made upon his assistant's 

 memory, with as good results. There was a single and curious 

 exception. During one of the experiments a cord in the appa- 

 ratus snapped ; this incident so distracted the assistant's memory 

 of a given tint that his reproduction of it was utterly at fault ; 

 but immediately afterwards he regained his usual average of 

 correctness. The reproduction of grays, that is, mixtures of 

 white and black, is attended, as might be supposed, with a some- 

 what larger average of error ; but the experiments on this point 

 are not yet complete. From what has thus been shown it is 

 evident that the memory of definite tints is fairly accurate, so that 

 it can be depended upon within certain limits. Hence the juxta- 

 position of tints to be compared in spectroscopes and other 

 optical instruments is not always necessary. The instruments 

 themselves can be made far less complicated and costly where this 

 feature of cons ruction is not required. Observers can be trained 

 to an accurate memory of tints and even of differences of lumin- 

 osity. Prof. Rood snowed also some apparatus for obtaining a 

 quantitative analysis of the effect of contrast upon adjacent 

 colours. It was shown, for instance, that the colour of a small 

 disk on a large ground was overwhelmed by its background to 

 the extent of 12 per cent. In the discussion on this paper, Prof. 

 Trowbridge, of Columbia College, stated that his students in 

 drawing, preparatory to a course of engineering, were required 

 first to make a draught from a model, and then, the next day, to 

 reproduce the draught from memory. Several of these drawing-, 

 with the duplicates from memory, were exhibited ; they gave 

 conclusive proof that the memory of form under such circum- 

 stances may be cultivated to a high pitch of accuracy. 



Prof. S. P. Langley gave a brief account of a portion of his 

 researches on the radiation of the solar atmosphere. These have 

 demonstrated the decline of heat-radiating power from the centre 

 to the edge in a certain series ; and also a decline of light- 

 radiating power in a totally different series, the li^ht near the 

 centre having a blue tinge while that of the outside edge is 

 chocolate red. The apparatus used in these researches was 

 exhibited. About thirty years ago Secchi ventured the assertion 

 that there was a marked difference of temperature between the 

 northern and southern hemispheres of the sun. Prof. Langley 

 afterwards disproved this by experiment, and placed the facts 

 before the French Academy. Somewhat recently two French- 

 men, Messrs. Cruls and Lacaille, announced to the Academy, 

 (through the Emperor of Brazil, who is a corresponding member) 

 that they had verified the original observations of Secchi. They 

 stated that the heat of the northern hemisphere of the sun was 

 to that of its southern, as 100 to 75. Prof. Langley has since 

 carefully repeated his experiments, and is satisfied that there is 

 not a demonstrable difference in the heat of the two hemispheres. 

 In the course of 400 observations he has found only fractional 

 differences of less than one per cent., and since there is no 

 systematic relation between these, they are to be ascribed to such 

 errors as we may reasonably expect. 



A second paper from Dr. Joseph Le Conte was read, on the 

 glycogenic function of the liver, being a continuation of a 

 paper on the subject read at a previous meeting and since pub- 

 lished. The theory which is advanced in these papers and 



