252 



NATURE 



[July 14, 1892 



weight was first clearly demonstrated as due to the attrac- 

 tion of the Earth, although mere surmises had been 

 propounded by early astronomers, and in " Troilus and 

 Cressida " we have — " As the very centre of the earth, 

 drawing all things to it." 



But Acts of Parliament on " Weights and Measures " 

 were extant hundreds of years before the first appearance 

 of the " Principia " ; and when the standard pound weight 

 was defined in these Acts, it was the lump of metal 

 preserved at the Exchequer that was described, and not 

 the pressure on the bottom of the box in which it was kept. 



13. Formerly, the words vis inertice, or inertia, were 

 used instead of the modern word mass (often used in 

 ordinary language as the equivalent of bulk). But it is 

 useful to notice that inertia is not always the same thing 

 as weight or mass, or even proportional to them. 



Thus the inertia of a body is increased by the presence 

 of the surrounding medium ; the inertia of a sphere 

 moving in a frictionless incompressible liquid is in- 

 creased by half the weight of the liquid displaced, and 

 of a cylinder moving perpendicular to the axis by the 

 weight displaced ; while an elongated projectile requires 

 rotation about an axis for stability of flight, in conse- 

 quence of its inertia being different for different directions 

 of motion. 



The inertia of a pendulum, or of the train in § 2, is in- 

 creased to an appreciable extent by the presence of the 

 surrounding air. 



Again, the inertia of a rolling hoop is twice its weight, 

 of a cyhnder is half again as great, of a billiard ball is 40 

 per cent, greater ; and the inertia of a bicycle, or of the 

 train we have considered in § 2, when the rotary inertia of 

 the wheels is taken into account, must be increased by a 

 fraction of the weight of the wheels and axles equal to 

 ^7^-, where a is the radius of a pair of wheels, and k the 

 radius of gyration of the wheels and axle about the axis 

 of rotation. 



For the same reason the centre of inertia does not 

 always coincide with the centre of gravity, or centre of 

 mass. The buffers of a railway carriage should be at the 

 height of the centre of inertia ; and this is easily seen 

 to be at a height 



V('+wS 



above the axles, -w denoting the weight of the wheels, W 

 of the body of the carriage, and h the height of its centre 

 of gravity above the axles. 



The recommendations of the A.I.G.T., in their 

 " Syllabus of Elementary Dynamics," will only serve to 

 widen the increasing gulf between theoretical treatises 

 and the Applied Mechanics which engineers use, unless 

 the Committee of the A.I.G.T. will set to work to invent a 

 totally new word, such as heft, to express the pull of 

 gravity on a given weight, as an equivalent of the French 

 ■woxdipesanteiir ; it is hopeless to attempt todegrade the, 

 old word weight into the subsidiary secondary meaning 

 so long as in commerce, and in the Acts of Parliament, 

 weight invariably means quantity of matter, copia 

 materice. A. G. Greenhill. 



APHANAPTERYX AND OTHER REMAINS IN 

 THE CHA THAM ISLANDS. 



IN a former letter I sent you some account of the find- 

 ing of the Aphanapteryx in the Chatham Islands. I 

 have now gone more carefully over the bones I collected 

 there, and some additional notes may not be without in- 

 terest. I find that, of the heads I have obtained, a number are 

 much larger than that of Aphanapteryx broeckei (Schlegel), 

 and are therefore rightly assigned, I think, to a distinct 

 species. The tarso-metatarsus, as figured by M. Milne- 

 Edwards, however, may, I think, prove to belong not to 



NO. I 185, VOL. 46] 



Aphanapteryx, ox at any rate not to a species with so robust 

 a tibia. I found several tarso-metatarsi in near relation to 

 the tibias and femora, and heads of A. hawkinsi, and they 

 are all without exception much shorter and stouter bones in 

 proportion to the tibiae and femora. Out of the same 

 strata which contained Aphanapteryx, I obtained a num- 

 ber of the bones of the skeleton of a Fulica very nearly 

 related to F. Jtewtoni. Like the Aphanapteryx bones, 

 they vary very much in size, some being equal, others 

 much larger than those of F. newtoni. So much so that I 

 am inclined to recognize them as different species, or at 

 least different races. The larger species I have named 

 F. chathamensis. The portions I have had before me are 

 the pelvis, the femur, the tibia, and metatarsus. I have 

 portions of a large ralline skull, which may be that of this 

 Fulica, but it is rather too imperfect to enable me to speak 

 more confidently at present. The tarso-metatarsi of this 

 bird agree much more closely with the tarso-metatarsus 

 assigned in M. Milne-Edwards's plate to Aphanapteryx. 

 Of the Aphanapteryx I possess the complete cranium, 

 femur, tibia, metatarsus, humerus, and pelvis. Among 

 the other interesting specimens so far identified, are the 

 humeri and pelvis of a species of Crow half as large 

 again as C. comix. They agree closely with those of a 

 true Co7'vus. I have designated it as Corvus morioriwi, as 

 I found some of these bones among the remains scattered 

 round a very ancient Moriori cooking-place, which had 

 become uncovered by the wind in the strata in which 

 Aphanapteryx occurs. Indeed, in this kitchen-midden I 

 gathered portions of the Apha?tapteryx, of a large swan, of 

 several species of ducks, and of a Carpophaga indis- 

 tinguishable from the species now living on the islands 

 — as'p&c\&s{Carpophagachathamica mihi') new to science. 

 I may say that it is easily distinguished from C. 

 novcB-zealattdia: by the breast-shield in both sexes being 

 altogether duller than, and not extending so far ventr ally 

 as, in the latter. The head, neck, and breast are of the 

 same colour — a dull green, with purple and green metallic 

 reflections when viewed with the bird between the light 

 and the eye. It is, however, most markedly distinguished 

 by the pale lavender colour of the external border of the 

 wings, the much paler colour of the lower back and rump, 

 and by the black on the under surface of the tail feathers 

 being prominent on all the rectrices except on the anterior 

 portions of the outer tail feather on each side, and passing 

 under the tail coverts in a broad wedge. Mr. Travers 

 relates that he was informed by one of the early settlers 

 on Pitt Island that he remembered the first appearance 

 of the pigeon in the islands. This statement cannot well 

 be accepted in face of the presence of the bird's bones 

 in a midden so ancient as that I have referred to above. 

 In the Aphanapteryx beds, I obtained also the portions 

 of a skull of a species of Columbidce, apparently of a 

 Columba, of which I can say little till I am in possession 

 of more material. I have obtained also bones of the small 

 hawk {Harpa), showing that it existed on the islands, 

 whereas it is now unknown there, although Circus 

 gouldi'is not uncommon. 



At about 3 feet below the floor of a small cave, which 

 the weathering limestone has deposited, I obtained por- 

 tions of a pigmy Weka {Ocydromus pygmoeus), and also 

 the limb bones of a rat. If they have been gradually 

 covered to this depth by the fall of particles from the 

 roof, as there seems no reason to doubt, their age must 

 be very great ; but whether that would take us back to a 

 date antecedent to the arrival of the Morioris in the 

 Chatham Islands is a more difficult question to answer 

 with our present data. 



So far, the birds of whose presence in the Chatham 

 Islands till now we have had no knowlege, are : Harpa 

 ?ferox, Nestor meridionalis and ? N. notabilis, Corvus 



[I ? CarJ)oJ>haga chathamensis oi'R.oX^as.cMAA, P.Z.S. 1891, p. 312, pi. xxviii. 

 —Ed.] 



