434 



SCIENCE. 



[N. S. Vol. XXII. No. 562. 



published in The lUs (1903, pp. 11-18, pi. I.), 

 by Professor H. H. Giglioli, entitled ' The 

 Strange Case of Athene chiaradice,' a curious 

 variant of A. noctua^ having black instead of 

 yellow irides, and some variations in the mark- 

 ings of the plumage from the normal form. 

 The facts, and the speculations thereon by Pro- 

 fessor Giglioli, are of much interest, and Mr. 

 Scott thinks they help to confirm his view of 

 the ease of the two forms of Helminthophila. 

 But the facts are not at all parallel, the nine 

 specimens of the abnormal owl being traced 

 back to, presumably, a single pair. This case 

 has the essential features of a ' mutant,' as 

 these peculiar owls were not the product of 

 the union of two species, and hence not ' hy- 

 brids.' In other words, it is what Giglioli 

 appropriately terms ' a case of neogenesis' 

 which might, should the progeny survive, con- 

 stitute a new species. A further history of 

 this case will naturally be awaited with great 

 interest. 



As already shown, I fail to see any good 

 basis for Mr. Scott's attempt to employ the 

 ' mutation ' theory in explanation of the case 

 of H. lawrencei and H. leucohronchialis, and 

 believe still that these xinstable and ever-vary- 

 ing forms are primarily the result of hybridity 

 between H . chrysoptera and H. pinus, with 

 which belief the known facts in the case are 

 wholly consistent. Dichromatism may play a 

 part, as several previous writers have sug- 

 gested. The two forms are known to inter- 

 breed with each other and also with the 

 parent stock, producing fertile offspring. They 

 thus far, also, have been found (with the ex- 

 ception of a few migrating birds) only in the 

 area where the breeding ranges of H. chrysop- 

 tera and H. pinus overlap. That they have 

 not been found throughout this overlapping 

 area is more than likely due to the absence 

 from it of a sufficient number of expert ob- 

 servers. No section of the country within 

 this range has a tithe of the expert field ob- 

 servers and collectors, proportionately to the 

 area, that have been working for years through- 

 out the limited district which has thus far 

 almost exclusively produced the known ex- 

 amples of these birds. There seems to be no 

 obvious reason why they should not occur 



sparingly Avestward over a narrow belt south 

 of the Great Lakes to Wisconsin, where thus 

 far they seem to have been almost wholly over- 

 looked. 



In taking up this subject, Mr. Scott appears 

 to have proceeded without a very clear con- 

 ception of either the essential facts of the 

 warbler ease or of the phenomena of ' mu- 

 tants.' Plis assumption of the recent rapid 

 increase of these forms rests on statements 

 that are both misleading and irrelevant. The 

 region of their occurrence is wholly outside of 

 the fields of research of the ornithologists he 

 mentions as evidence of the thorough knowl- 

 edge of the ornithology of this region he as- 

 sumes to have existed ' in the early part of 

 the last century,' while, as regards numbers 

 and methods, these early workers are not for 

 a moment to be coixipared with those of the 

 last few decades. Besides, it is only a few 

 experts, who have made these birds a specialty, 

 and know their haunts and notes, who have 

 any success in their discovery. The facts, as 

 already said, of the known relationships and 

 the instability of these forms, harmonize 

 poorly with the phenomena of mutations, 

 shown by de Vries in relation to plants, in 

 which the new forms arise with definite, and 

 stable characters, which they can transmit 

 without modification to an apparently endless 

 succession of generations. J. A. Allen. 



SPECIAL ARTICLES. 

 BATTERY RESISTANCE BY MANCe's METHOD. 



Among the many methods for measuring 

 battery resistance, one of the oldest, and ap- 

 parently least understood, is that known as 

 ' Mance's method.' As usually discussed in 

 text-books this method is described as being a 

 modification of Wheatstone's bridge, in which 

 the cell to be measured takes the place of the 

 unknown arm and the usual battery is re- 

 placed by a simple key. When opening or 

 closing this key produces no change in the 

 steady deflection of the galvanometer the 

 bridge is balanced and, ' therefore, the usual 

 relation of Wheatstone's bridge is satisfied.' 

 It is the object of this paper to show wherein 

 many writers have erred in this explanation. 



