822 



SCIENCE. 



IVou II., No. 47. 



never eould be reduced), but is some small fraction of 

 an ohm (say, .2 ohm), and suppose that there is a 

 single lamp of 140 ohms' resistance in circuit, and 

 that the electromotive force is 100 volts: then 

 140 

 140 o -^ 100 = 995 volts will be the fall of potential 



in the lamps, and only y volt in the armature. But 

 suppose that there are 70 lamps of the same re- 

 sistance (140 ohms) in circuit, instead of a single 

 one." then the external resistance will be reduced to 

 140 



70 



= 2 ohms, and the fall of potential in the lamps 



will only he „ o ^ 100 — ""I" volts, and 9,-^, volts in 

 the armature. 



Thus we see, that, when the number of lamps in cir- 

 cuit is increased from 1 to 70, the difference of poten- 

 tial available in the lamps is decreased from 99" to 

 901" volts, a reduction of almost one-tenth ; in conse- 

 quence of which the candle-power of the lamps would 

 be lowered at least one-third, and probably one-half. 

 Of course, variations in the brightness of the lamps 

 of one-third, or one-tenth, or even one-twentieth, 

 would not be permissible: therefore, in order to 

 maintain the required steadiness of the light, it is 

 necessary to raise the electromotive force of the 

 dynamo as more lamps are put on, and to lower it 

 as lamps are taken off. This is done by increasing 

 or diminishing the strength of current in the circuit 

 of the field-magnets by means of a resistance-box 

 interposed in the circuit. This regulation of the 

 electromotive force of dynamos by controlling the 

 resistance of the field-circuit may be, and in fact has 

 been, made automatic; but up to the present time it 

 has more generally been done by hand. 



In what has gone before, I have said nothing 

 about the resistance of the conductors which con- 

 vey the current from the dynamo to the lamps. The 

 effect of the resistance of any conductor which is 

 common to tioo or more lamps — one of the main con- 

 ductors, for example — is precisely the same as the 

 effect of the resistance of the armature, which has 

 been discussed above ; but when a conductor supplies 

 only a sinyle lamp, then it does not have this effect. 

 Of course there is a loss or fall of potential due to 

 the resistance of the individual conducting-wires of 

 each lamp ; and of course the fall of potential in the 

 lamp itself, and consequently its brightness, are there- 

 by reduced. But this resistance does not introduce 

 any irregularity : its effect in diminishing the light 

 of the lamps is constant. 



Let us suppose that a conductor having a resist- 

 ance of 140 ohms feeds a single lamp of 1.4 ohms' 

 resistance: then the loss in this conductor will be 

 1 % of the useful fall of potential. But suppose that 

 we now put 10 more lamps in circuit: then the loss 

 in the conductors will be increased to over 10%; and 

 assuming the useful fall of potential to be 100 volts, 

 with a single lamp in circuit, it will only be about 90 

 volts with 11 lamps. The candle-power of the first 

 lamp would drop at least 2.5 % or 30% when the other 

 10 lamps were added. Thus it is, that, in a multiple 

 arc system of electric lighting, any resistance which 

 is common to a number of lamps, whether in the 

 armature or the conductors, causes fluctuations in 

 the light of the lamps when other lamps are put on 

 or off ; whereas the resistance of the individual con- 

 ductors of each lamp produces a loss of potential 

 which is a constant fraction of the total potential, 

 but does not introduce any unsteadiness. 



F. B. Cbockkr. 



Osteology of the cormorcint 



With respect to Mr. Jeffries' criticism (Sciknck, 

 ii. 739) of my paper on cormorants, I beg to say that 

 the occipital style of the cormorant is not an ossifica- 

 tion in the tendon of any muscle ; that he is entirely 

 wrong in his view of the homologies of what 1 call a 

 . patella; and that, furthermore, I find myself misquot- 

 ed more than once. K. W. ShufeLdt. 



A dog plans and executes -with reference to 

 the future. 



Six weeks ago Prof. J. B. Thayer of this place re- 

 turned from Kee Heights, Dakota, bringing with 

 him one of a litter of eight pups raised by a slut of 

 the setter breed. The story which he relates to me 

 of this pup's mother is, it appears to me, worthy of 

 record. 



The good mother appears to have discharged her 

 arduous duties as only a mother can, and arrived 

 with her eight babes at the time when they should be 

 weaned. At this juncture, judging from the events 

 reported to have followed, she seems to have con- 

 ceived the idea that too many dogs were occupying 

 the same claim, and that a distribution was desirable. 

 Accordingly, she started one morning with three of 

 her pups, and was observed by Miss Rosa Cheney, 

 now of this place, running in the road toward their 

 claim at a rate which made it impossible for the pups 

 to keep pace with her. The dwelling where she lived, 

 and another shanty on the adjoining corner of an- 

 other claim, are situated one mile and three-fourths 

 from the dog's home. The mother reached the claims 

 in advance of her babes, but no sooner had they ar- 

 rived than she hurried on at her best pace. Miss 

 Cheney reports that " the puppies came up all out of 

 breath, and apparently too tired to contiinie; but the 

 smallest of the three followed on." Another claim 

 was reached three-fourths of a mile beyond; and 

 here Miss Cheney observed the mother stop until her 

 panting babe came up, when she immediately set off 

 again. A quarter of a mile beyond the last claim, 

 the mother was observed to make a third halt as 

 before, and then to pass on beyond the range of vision, 

 towards Ree Heights, with the puppy still following 

 her. Two days later the persistent mothy, with her 

 more persistent babe, was observed coming back ; and 

 Miss Cheney tells me that the little puppy appeared 

 almost dead from fatigue. 



Some days later the dog led off two ntore of her 

 pups, and succeeded in leaving them both; but in the 

 mean time the two puppies left the first day were i-e- 

 tiu'ned. A pup was also left at Professor Thayer's 

 claim, but was returned, and exchanged for another. 

 Both Professor Thayer and Miss Cheney assure me 

 that other efforts of the same kind were made by this 

 dog, but with what results they are imable to say. 



After the puppies had been distributed, they were 

 not forgotten; for the old dog used often to go and 

 play with them. Professor Thayer mentions one in- 

 stance of her coming and playing with the puppy left 

 at his claim until it was very tired, when she lay down 

 by the side of it; but, after it had gone to sleep, she 

 quietly walked to the opposite side of the house, and 

 then hurried away in the opposite direction from 

 home for a distance of about forty rods, when she 

 titrned and went directly there, thus showing quite 

 clearly that the thought of distributing her puppies 

 was still uppermost in her mind. 



What events may have awakened this desire on the 

 part of the mother, or what reasons she had for her 

 acts, we do not know; but in her own mind I have 

 no doubt the case was urgent and the way clear, if 



