46 FLYING MACHINES. that no broad law can be laid down as to any fixed relation between the surfaces and weight of birds ot various sizes. The fact seems to be that while their structures are gov- erned by the laws which limit the strength of materials (bones, muscles, feathers, etc.), yet there are differences in the resulting stresses, and in the consequent efficiency of the birds themselves, who are thereby led to adopt slightly different modes of flight ; and in 1884 Miillenhoff published an able paper, in which he divided flying ani- mals into six series, in accordance with the ratio between their weight and their wing surface, as well as their methods of flight. As the tables of De Lucy, Hartings, Marey and Miillenhoff are all easily accessible in print, they will not be repeated here ; but the following table is considered more valuable than any of them. It has been compiled from " L'Empire de l'air" of Mr. Mouillard, a very remarkable book, published in 1881, which contains descriptions of the flight of many birds and accurate meas- urements of their surfaces and weights. TABLE OF SUPPORTING AREAS OF BIRDS. Measured by L. P. Mouillard. Compiled by S. Drzewihcki. Scientific Name. Nyctinomous segypticus Upupa epops........... Cotile rupestris......... Budytes flava.......... Galerita cristata I...... Caprimulgus........... Galerita crisfata II...... Accipter nisus.......... Pteropus Geoffroyi...... Coracias garrulus....... Tringa canutus........ Falco dnnunculus....... Passer domesticus I..... Vanellus cristatus....... Passer domesticus II..,. Cy pselus apus.......... Larus melanocephalus I. Glareola torquata....... Larus melanocephalus II Common Name. Bat.4........ Peewit....... Swallow....... Wagtail .. .. Lark.......... Goatsucker... Lark.......... Sparrow-hawk. Bat........... Roller........ Knott ........ Falcen........ Sparrow...... Lapwing...... Sparrow..... Martinet...... Gull.......... Glareola...... Gull*......... Sq. Ft. per Lb. f.64 3.62 3.62 3-49 3.18 3-17 3.06 3.00 a.79 2.76 3.64 2.48 2.42 2.40 2.36 2-35 2.35 2.32 2.30 Lbs. per Sq. Ft, 0.131 0.276 0.276 0.286 0.315 0.3H 0.327 o-333 0.362 0.363 0.380 0.403 0.414 0.417 0.424 0.426 0.426 0.431 0.435 Corr'&p'ding speed for a plane at 30 Miles per hr 15.9 23.1 23 1 *3-5 24.6 24.6 25.1 25.3 26.2 26.5 27.0 27.9 28.3 28 3 28.6 28.6 28.6 28.8 28.9