282 



SCIENCE. 



[Vol,. II., No. 30. 



air very sultry, we have two causes; and it is only by 

 observation that we can find out its true manner. I 

 do not lay very much stress upon the electrical tbeory. 

 But it is an interesting point, to me, to notice that 

 flashes of lightning have been observed between these 

 two clouds, showing that they were differently elec- 

 trified, and that there was some plausibility for the 

 theory which I sent to the signal-service. 



Pruf. F. E. Nipher continued tills discussion the 

 nest day, as follows: One matter connected with the 

 effects of this tornado contained a point, it seems to 

 me, of sufficient interest to call the attention of ob- 

 servers to the matter, in case any one should have 

 an opportunity to observe the effect of a tornado 

 upon water. Mr. Ferrel, I think, in his description 

 of a tornado, states that we have a rising of the water, 

 forming a sort of cone in the centre of the tornado; 

 the effect being, of course, ascribed to the diminution 

 of pressure which is known to be there. In the 

 cyclone proper, where we have a large area, we have 

 a storm-wave as the principal element in the case, 

 and there is an upheaval of the water in the area of 

 low pressure. In the tornado it seems to me very 

 questionable whether that occurs. I base that upon 

 this observation: A smaller wind-whirl which was 

 observed by myself in northern Missouri, which was 

 ratlier violent though not destructive, — a column of 

 dust several hundred feet high being raised, — passed 

 out upon a pond of water five or six feet deep, and a 

 depression was formed in the water, extending to the 

 bottom of the pond, — an immense cup. The water 

 was revolving rapidly; and it was thrown into rota- 

 tion with a centrifugal effect, — the same effect as 

 when a vessel is whirled. It seems to me that this 

 is an element which has not been considered as it 

 should be. If the whirl is small, and you have not 

 only a diminution of pressure in the centre, but of the 

 whole body of the water, the friction producing a 

 rotation of the water, if the result is sulficienlly 

 small you might get a depression instead of an ele- 

 vation. I call attention to this, so that those who 

 may be fortunate enough to see a tornado on the 

 water may not take it for granted that it is all 

 known. 



As to the remarks of Professor Rowland in regard 

 to the possible electrical origin of a tornado, I know 

 that he was very careful to say that he did not think 

 any of the destructive effects could be ascribed to the 

 action of electricity. I gathered the idea that he 

 thought a tornado might originate in that way, — that 

 two electrified clouds will attract each other, and come 

 together; and he calculates the energy of the attrac- 

 tion which bodies can have for each other in air. It 

 seems to me that tlie simple observation that was 

 made by Mr. Hoy, together with another fact which 

 we know, — that when the discharge passes between 

 electrified bodies they are almost wholly discharged, — 

 would show that when that happens the cause for 

 that motion has disappeared. When these two clouds 

 approach, a spark passes, and the whole thing is 

 gone. So long as there is no spark passing, we know 

 very well that the attraction is very much less than 

 the maximum attraction of -ySis of an ounce on the 



square inch. I think, perhaps, that is a matter Pro- 

 fessor Rowland did not consider. It does not seem 

 to me at all likely that any such origin can be as- 

 cribed to the tornado. When it is developed, you 

 may have a rarefied column which may be very highly 

 rai'efied, connecting the earth with the upper regions, 

 wliich is precisely the reason that the lightning which 

 was observed in the case of the Racine tornado was 

 not accompanied by thunder. 



Prof. ,J. T. Lovewell said it occurred to him, from 

 his observation, that a good deal of care is necessary 

 in order that the observer may know exactly what 

 he sees. It was my fortune, said he, to witness a 

 small whirl at a distance of three or four miles. I 

 saw the funnel-shaped cloud descend toward the 

 earth, and it looked to me as though there were a 

 column of water. Many people who saw it spoke of 

 it as a waterspout. It might liave been water, for 

 aught that we could have said fi om our point of sight. 

 I immediately drove to the spot, and it appeared that 

 not a drop of rain had fallen in that track. The 

 whirl had been sufficient to overttirn a few stacks of 

 grain and hay, and a man was thrown about with his 

 team in the road. I think, if it had struck a body of 

 water, I should be slow to believe that it lifted any 

 solid column of water into the air one hundred feet. 

 It would have made a grand scattering of the water, 

 and a great deal of it would have been thrown up 

 into the air. I believe that a good deal of that which 

 is commonly ascribed to columns of water rising up, 

 and pouring down the sides in cataracts, is optical 

 illusion. I should be slow to take the testimony of a 

 person seeing them, unless he had his mind disabused 

 of the common notions about these waterspouts. So 

 far as their electrical origin is concerned, I quite 

 agree with Professor Nipher that it is not by any 

 means proven that electricity has any thing to do 

 with them, except that it is a necessary adjunct, of 

 course, to all such disturbances. 



A method for the calibration of a 

 galvanometer. 



BY B. F. THOMAS OF COLUMBIA, MO. 



A BATTEKT of any sort is joined in circuit with 

 a sensitive galvanoscope H, a galvanometer G, and 

 any variable resistance iJ. When the circuit is closed 

 at K, the current is so adjusted by varying R, as to 

 give the highest desirable deflection of the galvanom- 

 eter needle. The needle of U will be forced against 

 the stops. By means of magnets m and m, the needle 

 of II is brought back to zero. If these magnets and 

 the galvanoscope be undisturbed, the original current 

 strength will be indicated when the needle stands at 

 zero, whatever changes may have been made In the 

 circuit. If now the shunt S be connected at 1, 2, 

 and the resistance of the shunt is made equal to that 

 of the galvanometer (positively determined), and the 

 needle of H brought back to zero (by increasing iJ, 

 as insertion of the shunts lowers the total resistance 

 of the circuit, and therefoi'e increases the current 

 strength, deflecting H), a new deflection of tlie gal- 

 vanometer needle will be produced, the deflection 



