i88 



SCIENCE. 



[Vol. XI. No. 272 



Hessian troops. It was first announced in England two years ago 

 by Miss E. A. Ormerod, consulting entomologist of the Royal Agri- 

 cultural Society, and it has proved more or less injurious. It has 

 rapidly extended during the past two years, so that now it is found 

 on most portions of the eastern coast, extending up into Scotland. 

 In North America it has spread over the entire wheat-producing 

 country, having appeared in California during the past three years. 

 Dr. Riley thinks that all the evidence points to the importation of 

 the Hessian-fly into England from the continent of Europe, and not 

 from America. He is also of the opinion that on account of the 

 cooler summers and milder winters, and the lateness at which 

 wheat is sown in England, there is very little danger that the crops 

 will be injured there to any such extent as in America and in por- 

 tions of continental Europe. In fact, it is very injurious only under 

 conditions where two generations are pretty likely produced in the 

 same year ; and he is satisfied that in England, as a rule, only one 

 generation will be produced. 



The third of the insect pests of which Dr. Riley spoke was the 

 hop-plant louse, Phorodon humuli, of which the full life-history has 

 been learned within the past year. It hibernates at the present 

 season of the year. The little glossy, black, ovoid eggs of the 

 species are found attached to the terminal twig, and especially in 

 the more or less protected crevices around the bud, of different 

 varieties and species of plums, both wild and cultivated. From 

 this winter egg there hatches a stem-mother, which is characterized 

 by being somewhat stouter, with shorter legs and honey-tubes, 

 than in the individuals of any other generation. Three partheno- 

 genetic generations are produced upon plums, the third becoming 

 winged. This instinctively flies to the hop-plant, which is entirely 

 free from attacks during the development of the three generations 

 upon plums. A number of parthenogenetic generations are pro- 

 duced upon the hop, until in autumn, and particularly during the 

 month of September, winged females are again produced. This is 

 the pupifera or return migrant, and she instinctively returns to the 

 plum. Here she at once settles, and in the course of a few days, 

 according as weather permits, produces some three or more young. 

 These are destined never to become winged, and are true sexual 

 females. Somewhat later, on the hop, the true winged male, and 

 the only male of the whole series, is developed ; and these males 

 also congregate upon the plum, on the leaves of which, towards the 

 end of the season, they may be found pairing with the wingless 

 females which stock the twigs with the winter egg. Twelve gen- 

 erations may be produced during the year, but there is great irreg- 

 iftarity in the development of these generations, and the return 

 migrant from the hop is produced at the end of the season, 

 whether from individuals of the fourth or fifth generation, or of the 

 twelfth. Each parthenogenetic female is capable of producing one 

 hundred young (the stem-mother probably being more prolific), at 

 the rate of one to six, or an average of three per day, under favor- 

 able conditions. Each generation begins to breed about the eighth 

 day after birth, so that the issue from a single individual runs up 

 easily, in the course of the summer, to trillions. The progeny from 

 a single stem-mother may, under favoring circumstances, blight 

 hundreds of acres in the course of two or three months. 



The exact knowledge thus gained, said Dr. Riley, simplifies the 

 protection of the hop-plant from PJtoi'odon attack. He suggested 

 destroying the insect on the cultivated plum in early spring, and 

 the extermination of the wild-plum trees in the woods. The in- 

 troduction of the pest into new hop countries in the egg state upon 

 plum cuttings or scions may be avoided. Infection from one hop- 

 yard to another never takes place. 



ELECTRICAL SCIENCE. 



Electrical Energy from Carbon without Heat. 



A FEW years ago Mr. Willard E. Case brought forward a battery 

 in which an electric current was generated without the consump- 

 tion of the elements of the cell, the energy being derived from some 

 external source of heat. The electrodes were tin arid platinum im- 

 mersed in a solution of chromic chloride, which, at ordinar)' tem- 

 peratures, has no action on the plates. If the cell be heated, " part 

 of one of its elements, chlorine, leaves the chromic chloride, goes 

 over and temporarily combines with the tin, forming a proto-chlo- 



ride of tin." This action generates an electric current with an 

 electro-motive force of about .3 of a volt. When the cell is allowed 

 to cool, the tin crystallizes out again, and the cell is as it was before. 

 We have, then, a current of electricity the energy of which is ob- 

 tained from the source of heat applied to the cell, the possible etfi- 

 ciency of the arrangement being fifteen or sixteen per cent. For 

 many reasons this cell cannot be practically used ; but Mr. Case 

 has pursued the general subject, and, in a paper lately read before 

 the Institute of Electrical Engineers, he has brought forward some 

 extremely interesting and suggestive experiments. It is probable 

 that the ultimate sources from which electrical energy will be de- 

 rived are natural sources of power, — waterfalls, etc., and coal; the 

 conversion in the latter case being direct. For the former a per- 

 fected storage-battery is necessary ; for the latter, some means of 

 oxidizing the coal without the production of heat, the energy being 

 converted directly into electric currents. Mr. Case's experiments 

 in the latter field are as follows : •' In a glass cell containing sul- 

 phuric acid C.P. (specific gravity i.Si, temperature 75° F.) two 

 electrodes were immersed. — one of platinum, the other of lump 

 graphite. Only a slight electro-motive force was indicated, .007 of 

 a volt, due to the combination, the graphite acting as the positive 

 element. On the addition of a small quantity of chlorate of potas- 

 sium to the acid, the electro-motive force immediately rose to .8 of 

 a volt, the graphite being disintegrated after a time. This cell 

 polarized rapidly, which was partially prevented by mechanical 

 means. ... A method of exclusion was adopted to ascertain the 

 oxidant of this electrolyte : chlorine peroxide (ClOjl appeared to 

 be the only active agent. It is decomposed by the carbon, chlorine 

 being evolved with some oxygen. It was assumed that in this cell 

 graphitic acid (CnH^O^) was formed as the result of the chemi- 

 cal actions." Different forms of carbon were tried in the cell, giv- 

 ing a different electro-motive force for each form, varying from .3 

 of a volt to 1.25 volts. 



Mr. Case sums up the results as follows : " Undoubtedly the di- 

 rection of experiments in the future will be to find some cheap sub- 

 stance which will absorb oxygen from the air and give it up to the 

 carbon ; in fact, acting as a carrier of oxygen, so oxidizing it with- 

 out heat. And this is not improbable, as we already know of sub- 

 stances which do this, though giving a low electro-motive force : 

 thus, for instance, the ferric salts are reduced to ferrous by agitating 

 their solutions with carbon, being regenerated by absorbing oxygen 

 from the air. By pursuing this line of investigation, we can be sure 

 we are not ignorantly striving against any law of nature when 

 attempting to convert the whole potential energy of carbon into 

 electrical energy." 



If we take the energies of combination of different substances as 

 indicating approximately the electro-motive force obtainable from 

 the action, we will find, in looking at the tables giving energies cor- 

 responding to various chemical actions, that the greatest electro- 

 motive force we can hope for with batteries in which metals are 

 consumed does not exceed three or four volts. With the hydro- 

 carbons it is different : the energy in some cases is very great ; and 

 a battery in which part of the action consists of the formation of 

 some hydrocarbon, or the change from one hydrocarbon to another, 

 might give a much greater electro-motive force than any batter\- 

 with which we are acquainted. It is very probable that some one 

 will discover a practicable battery of the type Mr. Case has pointed 

 out. 



Maximum Efficiencv of Incandescent L.\mps. — Two 

 things are very well known about incandescent electric lamps : 

 their efficiency increases as we increase the current through them, 

 and their brilliancy, and their life decreases from the same causes. 

 There are two items of cost in electric lighting, — the cost of the 

 current supplied to the lamp, and the cost of renewal of the lamps 

 themselves. By running lamps at a very high candle-power, we 

 decrease the amount of current required per candle, but our bill for 

 breakage of lamps is correspondingly increased. Now, it is evident 

 that if we know the cost of the current and lamps, and the life of 

 lamps corresponding to different efficiencies, we can calculate the 

 least expensive way to run our lamps. This .Mr. Howell has done 

 in an excellent paper read before the American Institute of Elec- 

 trical Engineers. He has obtained, in the first place, the efficiency 

 of certain Edison lamps corresponding to different candle-powers 



