POPULAR MISCELLANY. 



421 



much of the same form as the greyhound, 

 and which it could hardly be questioned 

 was the source from which it sprang. As- 

 suming that the origin of the dogs could be 

 traced to these sources, the more modified 

 forms of the domestic animal were simply 

 the result of the selected breeding which 

 had given rise to similar modifications in 

 dogs as it had done in the case of pigeons. 

 Referring to the origin of dogs in general, 

 Professor Huxley noticed the discovery of 

 a fox-like animal of the Pleiocene period, 

 which was found near the Lake of Constance. 

 An animal, the cynodictus, lived in the up- 

 per Eocene period whose dentition was sub- 

 stantially that of the dog, and which ap- 

 peared to bridge over the wide interval that 

 separated the bears and animals of that 

 order from dog-like forms. Beyond that 

 period there was no distinct trace of dog- 

 like animals. By the application of ordi- 

 nary common-sense reasoning, which was 

 verified every day by experience, they were 

 driven to the conclusion that they could 

 only attribute the origin of these animals 

 to causes which operated in the existing 

 course of nature. This left them to the 

 simple alternative of the doctrine of evolu- 

 tion. He believed that small differences of 

 form slight modifications of one main plan 

 were amply sufficient to give rise to the 

 existing dog-like animals, and that these 

 modifications had actually taken place, start- 

 ing from the cynodictus. 



Efficiency of Lightning-conductors. Di- 

 rect evidence as to the efficiency of lightning- 

 conductors is afforded in a government re- 

 port from Schleswig-Holstein, which is re- 

 ferred to in a recent work on the subject 

 by Mr. Richard Anderson. Thunderstorms 

 are said to be more numerous in Schleswig- 

 Holstein than in any other part of central 

 or northern Europe, and the danger from 

 lightning is correspondingly increased. The 

 attention of the government insurance-office 

 was called to the fact that, in four out of 

 552 cases of claims on account of damage 

 from lightning arising in eight years, con- 

 ductors of approved design had been in use, 

 and an expert, Dr. Holtz, of Greifswald, was 

 appointed to inquire into the causes of fail- 

 ure. He found that, in every case where a 

 building provided with a conductor had been 



struck by lightning, the conductor was not 

 in an efficient state. Sometimes the point 

 of the rod was needlessly ornamented with 

 gilding, while the underground connection 

 with the earth, the very element of safety, 

 was neglected. In the absence of a proper 

 ground connection, the lightning-rod, instead 

 of being a protection, may prove the means 

 of attracting the discharge into the building. 

 A measure for the periodical testing of con- 

 ductors is suggested, for the detection of de- 

 fective constructions, interruptions of con- 

 ductivity by rusting or displacement, or of 

 other faults that may arise from time to 

 time. 



Atmospheric Currents and Carbonic Acid. 



M. Marie' Davy, of the Observatory of 

 Montsouris, France, has made a report of 

 observations which he has taken for four 

 years on the proportion of carbonic acid in 

 the air as it is related to the grand atmos- 

 pheric movements. The quantity of this 

 gas is found to vary from twenty-two to 

 thirty-six parts in one hundred thousand 

 parts of air. During the earlier observa- 

 tions, extending to December, 18*77, the 

 proportion of carbonic acid was below the 

 mean, and sometimes fell very low. In a 

 second period, from December, 1877, to 

 September, 1879, the proportion was con- 

 siderably above the mean. A third period 

 began in October, 1879, which was charac- 

 terized like the first period by a relative 

 weakness of proportion. The weakness be- 

 came remarkable in December. The sec- 

 ond period, in which the carbonic acid was 

 superabundant, was characterized by moist 

 weather with a predominance of the equa- 

 torial current over France, and embraced 

 two years of short crops. The first period 

 was characterized by an inferior extension 

 of the equatorial current, by less wet weath- 

 er and better crops. During all of the time 

 of the observations, the proportion of car- 

 bonic acid showed no variation to corre- 

 spond with the changes of the wind or the 

 indications of the barometer, thermometer, 

 and hygrometer. The fall of rain had no 

 definite effect on the proportion. It thus 

 appears that the proportion depends on the 

 general predominance of the equatorial cur- 

 rent, and not on the temporary changes of 

 weather. 



