32 



KNOWLEDGE 



[Februaky 1, 1894. 



being published in 1775. By trigonometrical measure- 

 ments the distance between two points, one north and 

 the other south of the mountain, was found, and from 

 this the difference of their geographical latitudes was got. 

 The true latitude of each point chosen was also determined 

 by astronomical observations. The diti'ereuce between 

 the true and geographical latitude of the two stations 

 depends on the amount by which the mountain deflects 

 by its attraction the plumb line which was used to 

 determine the vertical. This deflection was in an opposite 

 direction at the two stations, in one case towards the 

 north and in the other towards the south. The point 

 south of the mountain had its latitude made less than the 

 geographical latitude, because it was in the northern hemi- 

 sphere ; the point on the north side had its latitude made 

 greater. Thus, if the mountain had been symmetrical in 

 shape (and it was chosen because it approached to 

 symmetry) the difference of the astronomically found 

 latitudes would have been greater than the diii'erence of 

 their geographical latitudes by double the deviation pro- 

 duced on the plumb line by the mountain's attraction. 



By laborious measurements the form of the mountain 

 was next observed. As nearly as possible, its geological 

 composition and the specific gravity of its material were 

 determined, and then the attraction of this quantity of 

 matter of approximately known distribution and density 

 was compared with the attraction of the earth, which 

 exceeds the former in a known ratio. Maskelyne's result 

 for the density of the earth was 1-48 — four and a half times 

 denser than water ; but it is pretty certain from later and 

 better measurements that this value is considerably too low. 

 The great defect of this method is the uncertainty which 

 must occur as to the internal composition and structure 

 of the mountain itself and the surrounding country. 

 Cavities might be present m the hill, or places where the 

 matter was much lighter or much heavier than the 

 specimens taken from the surface ; and all such unknown 

 sources of error militate against an accurate determination. 

 The same method has been employed by James, at the hill 

 called Arthm-'s Seat, near Edinburgh. 



Another and different method of finding the earth's 

 mean density is that used by Airy. This consists in 

 comparing the time of vibration of a pendulum at the top 

 and at the bottom of a deep mine. The time of swing of 

 a pendulum depends on the attraction of the earth upon it. 

 At the bottom of a mine the outside layers of the earth 

 consisting of the mass contained in the outer skin, whose 

 thickness is the depth of the mine, cease to exert an 

 attraction on masses within — the attractions of separate 

 portions of this outer shell at opposite sides of the earth 

 mutually destroy each other. The attraction, then, on a 

 pendulum at a depth within the earth's surface consists of 

 that produced by the inner core, and at the bottom of the 

 mine we have come nearer to the core, but its volume and 

 mass is decreased as the cube of the radius, so that its 

 attraction is less than at the surface. On the other hand, 

 the attraction above ground consists of that due to the 

 core as well as that exerted by the shell. The observed 

 times of vibration of the pendulums give a means of 

 determining the amount of these two attractions — that of 

 the core and shell respectively. 



The volume of the outer shell is known, for it follows at 

 once from the known depth of the pit, and it has to be 

 assumed that the mass and density of the shell can be 

 determined from observations on the geological strata 

 passed through during the descent. Here comes in the 

 weak point of this method ; the true mass of the outer 

 skin must remain uncertain. 



Airy first attempted to apply this method at a mine in 



Cornwall, but met with various mishaps through accidents 

 to his apparatus, and it was not till after more than twenty 

 years from these first experiments that he, with the help 

 of numerous assistants, carried to a successful conclusion 

 his experiments, at the Harton coal pit, in the north of 

 England. Pendulums were made to vibrate at the upper 

 and lower stations. These were connected and compared 

 electrically, and thus the intensity of gravity at the top 

 and bottom of the mine was determined, and hence the 

 earth's density. 



The result of this experiment comes out considerably 

 higher than that by other methods, viz., G'56 for the 

 density of the globe, and we cannot have the same con- 

 fidence in this determination as in that of the results of 

 the Cavendish experiment, which do not differ much 

 amongst themselves. All that Airy claimed for his 

 method was that it was worthy of comparison with the 

 previous observations, and deserved to stand on an equal 

 footing with them. 



{To be continued.) 



THE COFFIN OF THE BUILDER OF THE THIRD 

 PYRAMID. 



By J. H. MtTcHiNER, F.R.A.S. 



IN the December number of Knowledge an interesting 

 article appeared under the above title, in which 

 Mr. Read calls the attention of English readers to 

 an article written by HeiT Kurt Sethe, published as 

 far back as 1892 in the Ziitschrift fur Ai/t/ptisrhe 

 Sp)-i(c/ie of Leipzig. Herr Sethe contends, on presumed 

 philological grounds, ^lat the coffin lid of 



Men-Kau-Eii, of the fourth dynasty, b.c. I O 

 3633, is not the original lid, but a later — 



,1 1 1 1111 . ULJ 

 era ^ 



coffin lid substituted for the original, and that it probably 

 dates from about the time of Tirhakah, b.c. 700. No 

 arguments are offered in support of this extraordinary 

 conclusion, beyond a general statement that the writing on 

 the lid is ideographic in character. Moreover, it is 

 asserted that the early texts are very deficient in these 

 ideographic signs, and that the name of Osiris written 

 with the ideographic prefix, as on the lid of this coffin, 

 cannot be found so written till the middle of the fifth 

 dynasty. 



Philological study of all ancient languages reveals that 

 among primitive peoples, however much divided by racial 

 or climatic conditions, the representation of ideas invariably 

 follows one common course of development. First, objects 

 are depicted, then sounds are depicted, and ultimately an 

 alphabetical system is evolved. Applying this law to the 

 hieroglyphical writing of the Egyptians, in order to gauge 

 the value of the argument of Herr Sethe, we are met by an 

 initial difficulty. At what date in the distant past are we 

 to ascribe to the Egyptians a system of pure picture-writing '? 

 of writing such as the primitive symbols of the Mexicans ? 

 Our knowledge of Egyptian history commences with 



^ ^ ]\lena, B.C. 4100. Only very recently has 



/ ^miiijj n I it been discovered how it is that Egyptian 



tradition observes a complete silence as to 

 history prior to this date. Mena was the Thinite Pharaoh 

 who succeeded in restoring a native dynasty after the 

 conquest of Egypt by the old Babylonian empire ; and, 

 it may be, the infinite pains taken by the Egyptians at a 

 later date to destroy all evidence of the long and hated 

 Hyksos interregnum was but a traditional repetition of 

 similar efforts on the restoration under Mena, after the 

 Babylonian conquest. We have no means of knowing the 

 duration of that conquest, nor the names and number 



