

548 



NATURE 



[April 7, 1892 



of the radiations emitted by an incandescent body of which the 

 emissive power is unity is expressed by the formula — 



I = io«-7 T-3iL° 

 T 



The temperatures employed range from 680" lo 1770°, and these, 

 with the observed intensity of radiation, have been used to plot 

 a curve. By extending the curve and measuring the intensity of 

 the radiation from the sun, an estimation of 7600° as the effective 

 solar temperature is obtained. The term effective temperature 

 is used to express that temperature which a body having an 

 emissive power equal to unity should possess, in order to send out 

 radiations of the same intensity as the sun. The real temperature 

 of the photosphere is higher than 7600°, because its radiations are 

 absorbed by the cooler solar atmosphere, and it may be, also, 

 because the emissive power of the sun is less than unity. 5 



Comet Swift, March 6. — The following ephemeris for this 

 comet is given in Astronomische Nachrichten, No. 3082, for 

 I2h. Berlin mean time : — 



i8q2. R.A. Decl. 



Wolf's Comet, 1891 II. — In Astronomische Nachrichten, 

 No. 3082, an ephemeris for this comet is given by Herr Dr. 

 Thraen, of which the following is an extract (i2h. Berlin mean 

 time) : — 



1892. R.A. Decl. 



h. m. s. o / // 



April 8 ... 5 53 19-13 ... -o 12 43-2 



„ 9 ... 5 54 49-39 ,- ... -o 7 21-8 



,, 10 ... 5 56 19-84 ... -o 2 7-1 

 „ II ... 5 57 50-48 ... +0 3 0-9 

 ,, 12 ... 5 59 21-29 ••• +0 8 21 

 ,, 13 ... 6 o 52-27 ... +0 12 56-6 

 „ 14 ... 6 2 23-43 ... +0 17 44-3 

 ,, 15 ... 6 3 54-78 ... +0 22 25-1 

 Periodic Perturbations of the Four Inner Planets. 

 — In the astronomical papers which are prepared for the use of 

 the American Ephemeris and Nautical Almanac (vol. iii., part v.), 

 most valuable computations of the periodic perturbations of the 

 longitudes and radii vectores of the four inner planets of the first 

 order as to masses are contributed. Prof. Newcomb, under whose 

 directions these computations were made, tells us in the intro- 

 ductory note that in the preparation of the fundamental data for 

 the new tables, all the coefficients, which are included in the 

 expressions for the general perturbations, were redetermined : 

 the values obtained for them agreed well with those obtained by 

 Leverrier, and prove that their accuracy is placed beyond doubt. 

 To eliminate any errors that might have been made, duplicate 

 computations were undertaken, and the results of them both are 

 given in the final expressions for the perturbations in longitude. 

 It may be stated that the complete theory is not here pub- 

 lished, the secular variations, perturbations of the latitude, and 

 those of long period in the longitude, not being printed, owing 

 to their unfinished state. 



N.P.D.'s observed with Greenwich and Washington 

 Transit Circles. — Prof. Newcomb, under whose direction 

 these computations were made, gives in vol. ii. part vi. of the 

 same series of papers just referred • to an interesting discus- 

 sion on the differences that have been found in these observa- 

 tions. Those made with the Greenwich circle cover a period 

 of thirty-six years, from 1851-87, while the Washington 

 observations are included in the years 1866-86. The author 

 has a firm basis here, on which he can rely, for in the 

 former series the same methods of reduction and observation 

 were in use for this entire period without interruption. He 

 inquires first of all into the conclusions which can be gathered 

 from the stability of the instrument, from both direct and reflec- 

 tion observations, and finds that the R-D corrections are mainly 

 due to flexure. The constant of refraction and the possible 

 periodic error due to those in the graduation of the circle 

 are then dealt with, together with corrections for reductions to 

 the equinox during the years 1851-56. The hypothesis of the 



NO. II 71, VOL. 45] 



secular change in the latitude is here considered as too improb- 

 able for acceptance with our present data, so that the apparent 

 variations are here supposed to be due to the changes in the 

 instrument or habits of the observers. In the section on the 

 latitude of the Royal Observatory, he finds that the co-latitude 

 derivable from observations of the four polar stars during the 

 period 1877-86 is greater by o"-3i than that derivable from 

 observations of all circumpolar stars. At the conclusion of this 

 investigation he gives a table showing the corrections to the 

 north polar distances, derived annually from the observations 

 with the Greenwich transit circle, to reduce them to the instru- 

 mental standard of the present paper, and the Pulkowa refractions. 

 Washington Observations, 1887.— All the observations 

 which were made during the year 1887 at the United States 

 Naval Observatory are included in this volume. The intro- 

 duction, besides giving the report of the Superintendent on the 

 state of the Observatory generally, contains all the detailed infor- 

 mation relative to the methods of computing the observations 

 made with the transit circle, meridian transit instrument, and the 

 26- inch and 9-6-inch equatorials. The principal work of the 

 transit circle during this period has been upon the sun, moon, 

 and planets, and miscellaneous stars. These last, included stars 

 of the American Ephemeris for clock corrections, &c. ; stars 

 whose occultations were observed at this Observatory, and by the 

 various American parties that observed the 1874 transit of 

 Venus ; those selected for standard stars in the formation of the 

 catalogue made from 1846-49; and stars of the B.A.C. be- 

 tween 120° o' and 131° 10' N.P.D. that have not been observed 

 three times in R.A. and declination at Washington. The 

 meridian transit instrument was devoted to the determination of 

 the errors of the standard mean time clock in connection with 

 the transmission of time, and 1645 transits were taken. The 

 clock's rate was found satisfactory, its variations following closely 

 those of the barometer. The 26-inch and 9"6-inch equatorials 

 have been also used, the former for observations of double stars 

 and small stars in the Pleiades, the latter for comets. Besides 

 these, many other magnetic and meteorological observations 

 are recorded, but a brief account of them will be found in the 

 notes. 



FERTILIZATION OF THE CASUARINACE^. 

 "CpEW recent articles in botanical literature can compare in 

 -'- interest and importance with that contributed by Dr. Mel- 

 chior Treub to the tenth volume of the Annates du Jar din 

 Botanique de Buitenzorg, "On the Casuarinacece, and their 

 Position in the Natural System." The. startling announcement 

 is made of the occurrence of a mode of fertilization of the ovule 

 essentially different from that which takes place in other flowering 

 plants. 



The species of the genus Casuarina, which alone make up the 

 order, are about twenty-three in number, and are trees, nearly 

 all natives of Australia, where they are known as "beef-wood 

 trees," characterized by their jointed, almost leafless branches. 

 From the catkin-like inflorescence of very imperfect flowers, 

 they are generally placed among Incompletse or Monochlamydeaj, 

 near to Myricacese and Juglandaceee. The female flower is 

 composed of two carpels, without either calyx or corolla, and 

 has at the base an ovarian cavity, in which are formed (in 

 C. suberosa) the two ovules with parietal placentation, but con- 

 nected from the first with its summit by cords of cellulose. 

 Corresponding to the style in most plants, is an axial mass of 

 tissue which M. Treub calls the stylar cylinder, surrounded by 

 a peripheral region containing tracheides, and terminating in 

 two elongated stigmas. The two ovules are unequal in size, 

 and coalesce in their growth by their placental portions ; the 

 connection between them and the base of the stylar column is 

 called the bridge ; they are also connected with the base of the 

 ovarian cavity by their funicles. 



The processes which take place within the ovule up to the 

 time of the formation of the embryo-sac are very different from 

 those hitherto observed in Angiosperms. Several large hypo- 

 dermal cells, the archespore-cells, at the summit of the nucellus, 

 divide tangentially ; and two of the cells thus produced towards 

 the inner side, the primordial mother-cells, divide further, giving 

 rise to a thick cylinder of large cells occupying the centre of the 

 nucellus, the sporogenous tissue, surrounded by flattened cells 

 corresponding to the " Tapetenzellen " of Goebel. The cells 

 of the sporogenous tissue are equivalent to the mother-cells of 

 the embryo-sac in other Angiosperms. These cells divide trans- 

 versely into large megaspores (macrospores) ; the small inactive 



