246 REPORT ON THE TRANSACTIONS OF THE SOCIETY OF 



observations made by hini on the habits of Mexican birds, illustrating 

 many facts regarding them which had escaped the attention of former 

 travellers. To M. Duby we were indebted for a report on the micro- 

 scopic researches of M. Amici relative to the constitution of the 

 muscular fibre. 



The investigations of which we have been speaking, however 

 special they may be, are none of them deficient in point of general 

 interest, whether as forming necessary links in the great chain which 

 binds together all the phenomena of nature, or because, considered 

 in themselves, they reveal some of the mysteries, every day more 

 remarkable, of the physical world. But this is not the only advan- 

 tage derived from the introduction of specialty into the study of the 

 sciences; one still "more considerable is that from this very specialty 

 there spring up between the different parts of those sciences new and 

 more intimate relations, in virtue of the greater perfection introduced 

 into researches. This connexion is particularly striking in animal 

 physiology, to such a degree, indeed, that sometimes we know not to 

 what branch of the sciences, physical or natural, we ought tf) refer 

 such or such an investigation. Is it to physiology or to physics that 

 the researches of MM. Thury and Claparede belong? the former on 

 the amount of mechanical force expended in walking, the latter on 

 the horopter. Whatever the place to be assigned them, we must 

 not omit them in this report, as the authors have communicated them 

 to the Society. 



M. Thury has found 7.2 kilogranietres as the value of the labor 

 performed by a man for every metre of distance which he travels, 

 answering to 10 or 12 kilograrnetres a second, according as the -daily 

 course is 8 or 10 leagues, the mean weight of the body being fixed at 

 65 kilograms. He deduces from his calculation that the longest 

 line over which a man can pass in a day on a horizontal level, without 

 permanent exhaustion of his force, is 48,000 metres, (157,473.6 feet,) 

 and that the greatest vertical height a man can attain, under the same 

 conditions, in ascending along an inclination of ^, is 4,000 metres, 

 (13,122.8 feet.) 



M. Claparede communicated a series of experiments designed to 

 show that the form of the horopter^ is different from that which, as 

 a consequence of the investigations of M. Meissner, German physiolo- 

 gists at present assume it to be. The horopter, as Meissner con- 

 ceived, is in a majority of cases a right line inclined on the plane of 

 vision of a quantity which varies with the distance of the point of 

 view. After demonstrating by conclusive experiments that this deter- 

 mination is erroneous, and that the line experimentally found by 

 Meissner is always perpendicular to the plane of vision, M. Claparede 

 believes himself authorized to conclude that this lino belongs to a 

 horopteric cylindrical surface, having for its base the horopteric cir- 

 cle of Pierre Prevost, rejected by M. Meissner. Subsequent experi- 

 ments have convinced him that the horopter is really formed but of 



s The surface of single vision corresponding to any given binocular parallax is called the 

 horopter. — (See Nicliol's Encyclopedia of Physical Science ) 



