20 



SCIENCE. 



[Vol. XII. No. 2l 



unexpected places, and passengers in a train may feel a shock be- 

 ■cause a charge has struck the rails. In powder-magazines it is ap- 

 parent how dangerous this lawless sparking tendency may be ; for 

 even the hinge of a door may furnish opportunity for some trivial 

 spark sufficient to ignite powder. By no means should high rods 

 be stuck up to invite a flash to such places. Build them, or line 

 them, with connected iron, barb them all over the roof, connect 

 them to the deep ground in many places, and but little more can be 

 done. 



These electrical oscillations and overflows, which it is easy to set 

 'Up in a charged conductor, manifestly explain what is known as the 

 'return-stroke.' This fact — that a discharge from anyone point 

 of a conductor may cause such a disturbance and surging as to 

 precipitate a much longer flash from a distant part of it — at once 

 .accounts for any ' return' stroke ' that has ever been observed. 



It is for this reason that it is possible that a tall chimney or other 

 protuberance in one's neighborhood may be a source of mild dan- 

 ger ; inasmuch as if it is struck it may be the means of splashing 

 ■out some more discharges to other smaller prominences, which 

 ■otherwise were beyond striking distance. 



Finally, is it possible for the interior of a thoroughly enclosed 

 metal room to be struck ; or, rather, can a small fraction of a light- 

 ning-flash find its way into a perfectly enclosed metal cavity, for 

 instance, a spark strong enough to ignite some gun-cotton in a 

 -metal-covered magazine which might happen to be struck ? 



The application of the laboratory experiments to powder-maga- 

 zines is, that, if any conductor (like a gas-pipe) pass out of the 

 building before being thoroughly connected with its walls, it is pos- 

 sible for a spark to pass from something in the interior of the build- 

 ing to this conductor whenever a flash strikes the building. 



The complete and certain protection of buildings from lightning 

 is by no means so easy a matter as the older electricians thought it. 

 In many cases we may be content to fail of absolute security, and 

 be satisfied with the probable safeguard of a common galvanized 

 iron rod or rope. But for tall and important buildings, for isolated 

 chimneys and steeples, and for powder-magazines, where the very 

 best arrangement is desirable, what is one to recommend } Profes- 

 sor Lodge sees nothing better than a number of lengths of common 

 telegraph-wire. He thinks a number of thin wires far preferable to 

 a single thick one ; and their capacity must be increased when pos- 

 sible by connecting up large metallic masses, such as lead roofs and 

 the like. But the connection should be thorough, and made at 

 many points, or sparks may result. Balconies, and other promi- 

 nent and accessible places, should not be connected. 



The earth should be deep enough to avoid damage to surface- 

 soil, foundations, and gas and water mains. As to the roof, he 

 would run barbed wire all round its eaves and ridges, so as to ex- 

 pose innumerable points, and the highest parts of the building must 

 be specially protected ; but he would run no rods up above the 

 highest point of the building, so as to precipitate flashes which else 

 might not occur, in search for a delusive area of protection which 

 ■has no existence. 



The conductors must not be so thin as to be melted or defla- 

 grated by the flash ; but melting is not a very likely occurrence, 

 and, even if it does occur, the house is still protected. The dis- 

 charge is over by the time the wire has deflagrated. The objec- 

 tion to melting is twofold : first, the red-hot globules of molten 

 metal, which, after all, are not usually very dangerous out of doors ; 

 and, second, the trouble of replacing the wire. The few instances 

 ordinarily quoted of damage to lightning-conductors by a flash do 

 not turn out very impressive or alarming when analyzed. 



MENTAL SCIENCE. 



The Nature of Muscular Sensation. 



The active side of psychic life is represented by movements. 

 The study of the w.ays and means by which these movements are 

 brought about, are co-ordinated and directed to useful ends, forms 

 one of the most important chapters of physiological psychology; 

 but the elements that enter into conscious motion are so numerous, 

 and so intricately connected, that our knowledge of the process is 

 as yet very defective. It has been well said that the clear and defi- 



nite statement of a problem is a long step towards its solution. 

 While recent research has not succeeded in definitely explaining 

 the nature of the sensations connected with movements, it has 

 cleared the problem of many misconceptions which had attached to 

 it, and called attention to those points from which a final solution may 

 be expected. M. Binet has recently brought together the various 

 aspects of the problem, and added thereto an ingenious suggestion 

 towards their further elucidation (Rcinie P/n'losop/ngue, May, 1888). 



The first distinction that M. Binet emphasizes is that between 

 the consciousness of a movement and that of the co-ordination of 

 the muscles necessary to make it. The latter does not enter into 

 the psychic aspect of movement at all. We may be, and usually 

 are, unaware of the simultaneous and orderly contraction of the 

 various muscles necessary to perform a useful act, and yet be per- 

 fectly able to do the act. It is the mental conception of the finished 

 act that guides the muscles and gives unity to the movement. Our 

 problem deals only with the methods by which we become aware 

 that our muscles have obeyed the mandate of our will. 

 ■ The simplest source of such knowledge is that obtained 

 through the eye. We know that a movement has been accom- 

 plished, because we see it. Again, in speaking, we know that the 

 muscular mechanism of articulation has acted properly, because 

 we hear the resulting sound. The voices of speaking deaf persons 

 are usually harsh, owing to the lack of the corrective power fur- 

 nished by the ear. But, even with the eyes closed, we have quite 

 a definite knowledge that the desired movements have been pei- 

 formed. The general sensibility, the feeling of effort as shown in 

 the change of respiration, etc., the dermal sensations produced at 

 joints, and the feeling of the shortening of muscles, — all contrib- 

 ute to the result. We are powerless to analyze the several roles 

 played by these factors by observing actions in ourselves ; but 

 here pathology helps us out of the difficulty, and shows what 

 psychic factor is deranged when a physiological function is 

 lost, as will be touched upon later. Again, this latter class of 

 sensations can learn to control movements which at first require 

 the aid of vision. Walking is a conspicuous example of such. All 

 these factors have the one point in common, that they act after the 

 muscles have contracted. They are due to impressions proceeding 

 inwardly, centripetally, to the brain, and thus informing us what 

 has been done. 



The question has been raised, however, whether we have not 

 knowledge of movement centrifugally before the action takes 

 place ; whether we have not an outgoing feeling of expended 

 energy suited to the act in question. This view has been sup- 

 ported by many illustrious names, and it has been negatived with 

 equally good authority. The objectors call attention to the fact 

 that there is such a thing as a motor image formed from former sense- 

 impressions, and that this is sufficient to call up the proper mental 

 antecedent upon which the motion ensues. This tells us how 

 much energy to discharge, leaving the rest of the factors to take 

 effect when the action is done. 



Pathology calls attention to cases in which the tactile sensibility 

 is destroyed, hoping to draw important conclusions from the inter- 

 ference that this causes with voluntary movement. When such a 

 patient performs a movement, he has only the visual sensory image 

 to guide him ; and, if this be taken away by blindfolding him, what 

 will happen ? This is the important test ; but it is not unambig- 

 uous in its interpretation. Most patients will do an action at com- 

 mand with their eyes closed nearly or quite as well as with their eyes 

 opened, the movements in question being those of an anaesthetic 

 limb. They write with the feelingless hand as well as normally. 

 From this observation we can at once conclude that the power of 

 co-ordinating movements, and the consciousness of the motion, are 

 two different things ; for these same patients can have their limbs 

 moved for them without their knowing it, thus showing that the 

 centripetal part is interfered with. Another class of patients, 

 however, are reduced, by closing their eyes, to a condition of almost 

 complete motor impotence. In spite of persistent exhortations, 

 they cannot take one hand in the other, touch their forehead, and 

 so on. The upholders of one side of the question emphasize the 

 former result, arguing that the centripetal sensations are not suf- 

 ficient to direct motion (for here they are lacking), and thus show 

 the necessity of assuming a consciousness of outgoing energy, an 



