September 5, 1901] 



NA TURE 



459 



anJ the air was motionless. The shade temperature reached 

 40°'5 C. in the course of the day. Time was taken as portions 

 of 5 cubic centimetres were distilled. The shortest fime in 

 which this quantity passed was 3m. 20s. This is at the rate of 

 l"5 c.c. per minute, and it occuried twice in the forenoon, 

 namely, at loh. 37m. and at iih. 23m, As the collecting area 

 of the reflector was 904 square centimetres, this corresponds to 

 i6'6 c.c. distilled per minute per square metre. If we apply 

 a correction for 20° zenith distance it becomes 1704 c.c. The 

 evaporation of 17 '04 grammes of water at 100° C. requires 

 91 16 gr.' C. of heat, so that the heat actually collected and 

 used in making steam was at the rate of 91 16 gr.° C. per square 

 metre or o'9ll6 gr.° C. per square centimetre per minute. 

 Converting 91 16 gr." C. into work at the rate of o'425 kilo- 

 gramme-metres per gramme-degree, we obtain as the realised 

 working value 3875 kilogramme-metres per minute or 0^87 

 horse-power per square metre. The reflector consists of one 

 mirror inclined at an angle of 45' to the axis of the instrument. 

 This mirror throws all the reflected rays normally on the sur- 

 face of the axial boiler. The larger mirror outside and the 

 smaller mirror inside of this one throw their reflected rays in- 

 clined at small angles to the normal. Taking all the reflected 

 rays together their mean normal component is 94 per cent, of 

 the total reflected rays. It is therefore legitimate to increase the 

 above figures in the proportion of 94 : 100, giving 0-93 horse- 

 power or 9700 gr.° C. per square metre per minute. The 

 mirrors are not perfectly reflecting, nor is the blackened surface 

 of the boiler perfectly absorbing. An allowance of 7 percent, 

 for these deficiencies will not be thought extravagant, and we 

 have in round numbers the work-value of the sun's vertical 

 rays on the surface of the earth at or near the sea-level as 

 I horse-power per square metre ; the equivalent of this in heat 

 is io,3CX) gr.° C. per square metre per minute, or I '03 gr." C. 

 taking the square centimetre as unit of area. 



Mr. Michie Smith informs the writer that the highest rate 

 which he has observed is i 754 c.c. distilled per minute at a 

 height of 7000 feet above the sea. This is exactly seven-sixths 

 of the maximum rate observed on the banks of the Nile. If we 

 imagine that in the most favourable circumstances the radia- 

 tion as determined in Egypt might be improved in this propor- 

 tion we get I '17 horse-power per square metre and I '202 gr. " C. 

 per square centimetre per minute as a value of the heating power 

 of the sun at the sea-level, which is probably very near the 

 truth. 



Comparing these results with those already quoted, we see 

 that they agree with Crova's summer values as determined at 

 Montpelier and lie midway between Vallot's (1 891) values for 

 Mont Blanc and Chamonix. We arrive therefore at the con- 

 clusion that the rate at which the surface of the earth at the 

 level of thel sea receives heat in the most favourable circum- 

 stances from the vertical sun is I -2 gr.° C. per square centimetre 

 per minute, or fi7 horse-power per square metre. In dis- 

 cussing questions of terrestrial physics it would not be prudent 

 to postulate a more abundant supply. 



If we ascribe to the atmosphere a coefficient of transmission 

 no greater than two-thirds, the value of the solar constant, or 

 the heating power which the sun's rays would exert on a sur- 

 face of one square centimetre exposed to them for one minute 

 at a point on the earth's orbit, is I '8 gr.° C. As the trans- 

 mission coefficient is probably greater than two-thirds, the value 

 of the solar constant is probably less than I '8. Vallot, by 

 giving effect to the rate of absorption actually observed in the 

 air separating his two stations, arrives at 1 7 gr." C. as the 

 most probable value. These values are in substantial agree- 

 ment with the older ones, such as those of Herschel and 

 Pouillet ; but there is a feeling at present that not much weight 

 is to be attached to these results, and much higher figures 

 seem to be more readily accepted. In a recent work, " Strah- 

 lung und Temperatur der Sonne," p. 38, T. Scheiner sums up 

 the discussion of this subject by giving 4 as the most probable 

 value of the solar constant. 



As we have .seen, the heat which arrives at the sea-level has 

 to support the temperature of the land and that of the sea ; it 

 has also to supply the energy for all the movements of the 

 ocean ; it has to warm and expand the air, and to furnish the 

 latent heat represented by the aqueous vapour in the atmo- 

 sphere, and it is mainly accountable for winds and storms. 

 All this is maintained on less than f5 gr. ° C. per square centi- 

 metre per minute. But when the above catalogue of functions 

 has been repeated, there is nothing left to be accounted for. If 



NO. 1662, VOL. 64] 



the sun's rays enter at the top of the atmosphere with an intensity 

 of 4 and come out at the bottom of it with an intensity of only 

 I 5, how is the loss to be accounted for ? It represents nearly 

 double the energy which reaches the sea-level and produces 

 such far-reaching effects. If it really entered the atmosphere it 

 must be still there, either as heat or as its equivalent. But we 

 know that the air is not made appreciably warmer by it, and 

 we see no mechanical manifestations which can in any way be 

 put forward as an equivalent. We conclude therefore that there 

 is no excess of heat of this order to be accounted for, conse- 

 quently values of the solar constant of the order of 4 are 

 exaggerated. J. V. Buchanan. 



REFLEX ACTION AND INSTINCT} 

 TN the Paris Jmtrnal of Anatomy and Physiology of 1869 

 there was reported by Robin an experiment on the body 

 of a criminal whose head had been removedjan hour previously, at 

 the level of the fourth cervical vertebra. The skin around the 

 nipple was scratched with the point of a scalpel. Immediately 

 there ensued a series of rapid movements in the upper extremity 

 which had been extended on the table. The hand was brought 

 across the chest to the pit of the stomach, simultaneously with 

 I the semiflexion of the fore-arm and inward rotation of the arm, 

 a movement of defence as it were. 



Probably none of us have seen quite so impressive an illustra- 

 tion of reflex action as the above, but most of us have watched 

 the experiment in which a frog, having been decapitated and 

 a drop of acid having been applied to its skin, the foot of the 

 same side is brought up to wipe away the acid, and if this foot 

 be cut off, alter some ineffectual efforts and a short period of 

 hesitation, the same action will be performed by the foot on the 

 opposite side. These symptoms of apparently purposive action 

 on the part of a brainless body have always struck me as most 

 strange. 



Some four years ago I had the privilege of reading to you a paper 

 on memory, from which I will now quote : — " When we attempt 

 to acquire some new feat of manual dexterity, involving a series 

 of combined muscular movements, such as a conjuring trick, we 

 find that, when first attempted, each movement has to be thought 

 out, and the whole is effected with difficulty. Every time that 

 the process is repeated the action becomes more easy ; each 

 movement of the muscles involved follows its predecessor with 

 greater readiness, and at last the trick becomes apparently one 

 action, is performed without thought, and may be said to be 

 automatic. The nerve structures involved have acquired a per- 

 fect memory of what is required of them ; each takes up its 

 part at the proper moment, and hands on in succession an inti- 

 mation to its neighbour that it is time to transmit the expected 

 impulse. Nerve centres have been educated. An organic 

 memory has been established." 



I went on to give instances in which, by frequent practice, 

 actions had become so habitual as to take place on the applica- 

 tion of the stimulus without the will of the individual, and even 

 contrary to his wish. I gave as an illustration the story of the 

 I old soldier who was carrymg a pie down the street, when some 

 I one mischievously crying " Attention ! " down went the soldier's 

 hands to his trousers seams, and down went his dinner in the 

 mud. 



Let us apply this effect of constant practice to the case in 

 question. The frog has a smooth, soft skin, unprotected by hair 

 or scales. His haunts are stagnant water which swarms with 

 injurious insects and other enemies ; or the banks of ponds and 

 streams abounding in sticks and stubs. From the time when 

 the first progressive tadpole protruded his incipient legs, the 

 race of frogs has been brushing away irritating substances. 

 The nerve cells of their spinal cords have established such re- 

 lations that, whenever a sense of irritation is conveyed to sensory 

 cells, motor cells in connection are brought into action, and a 

 complicated muscular movement follows, without the necessity 

 of the interference of the will. 



We may compare the association of nerve cells in the spinal 

 cord to a group of men highly drilled in particular evolutions. 

 Each individual cell of the group maintains relations with others 

 near it by some one or more of its many arms. Upon the receipt 

 of the intimation through sensory nerves and cells that there is, 

 something burning a particular portion o the frog's skin, motor 



1 A paper read before tlie Derby Medical Soc ety b W. Benthall, M.B., 

 on .April 9, 1901 



