imposed upon this some other disturbance which causes a slight departure from the perfect regularity of the curves. This disturbing effect is probably due to the fact, that, as it is difficult to keep the pitch of the notes given by the siren absolutely constant, they had departed somewhat from their proper values at the moment when the photograph was taken, and thus forced vibrations of a pitch slightly different from that of the tuning fork were added to those corresponding to its natural period. Having finished experiments on the difference-tone, we proceeded to photograph effects produced by the summation tone. The two notes used were obtained from the 9 and 12 rows of holes of the upper box of the Helmholtz double wind siren. It is easily seen that, to give a summation tone of 64, the disc must be revolving 64/(9+12) 3.048 times per second. To obtain this rate of rotation we used a stroboscopic method. On the upper surface of the lower box of the siren, we affixed a star-like disc with 18 rays, and viewed it through slits carried by a fork having a frequency of 27.4. When the star appears stationary, the disc is revolving at the desired rate, for 18 x 3.048 27.4 x 2 approximately. We have taken photographs of the steady bands when the siren has been going at the proper speed, and one set of holes open only. These are exactly like the steady bands obtained in the former cases. On sounding the two notes together the summation tone is produced, and we have photographed it in the manner already described. Figs. 7, 8, and 9 show some of the photographs obtained. In fig. 9, where the amplitude of the vibration of the bands is large, the plates used were not sufficiently sensitive to photograph them when moving through their mean positions. When the bands are in their extreme position and therefore at rest, the exposure is inversely proportional to the velocity of the plate. But when the bands are passing through their mean position, the exposure is inversely proportional to the velocity found by compounding the velocity of the plate with the velocity of the bands in a direction at right angles. If the amplitude is large enough, this velocity may be so great as to render the time of exposure too small to affect the plate. This phenomenon is slightly noticeable in fig. 5, and is very well marked in figs. 8 and 9. In conclusion, we wish to thank Mr. Cameron for assisting us in taking some of the later photographs, and Mr. Chapman for the help he has given us in preparing the lantern slides and prints. 400 Cytological Features of Fertilisation, &c., in Pinus silvestris. "On the Cytological Features of Fertilisation and related (Abstract.) This paper gives a fairly complete account of the minute cytological details of the act of fertilisation and of the processes surrounding it, from the formation of the ventral canal cell up to the period of cellwall formation at the base of the egg. As the oosphere nucleus, after separation of the nucleus of the ventral canal cell, moves rapidly back towards the centre of the egg, it increases greatly in size, as described by Strasburger. This increase in size is shown to be due to the appearance in the nucleus of a peculiar metaplasmic substance, which fills up the nucleus, and, owing to its attraction for stains, ultimately obscures the chromatin. The mature female nucleus, which is sometimes large enough to be visible to the naked eye, exhibits merely an uniformly staining reticulum composed chiefly of metaplasmic substance, with one or more nucleoli. By the rupture of the closing membrane of the well-marked pit at the apex of the pollen tube, almost the whole of the contents of the lower part of the tube pass over into the oosphere. At this stage all the four nuclei, together with a considerable number of starch grains from the pollen tube, are to be seen lying in the cytoplasm of the egg. Cytoplasm from the pollen tube must also necessarily pass over, and with it the plastid-like structures to be seen earlier in the cytoplasm of the generative cells. The behaviour of the four nuclei in the egg was carefully followed; the stalk cell nucleus, the pollen tube nucleus, and one generative nucleus remain at the apex of the egg, near the point of entry, and ultimately become disorganised. The other generative nucleus, which possesses distinct nucleoli, as does also its sister nucleus, advances very rapidly towards the female nucleus, increasing somewhat in size and in mass of staining material on its way. After coming in contact with the much larger female nucleus it gradually penetrates the substance of the latter until it is almost completely enclosed within it, but breaking down of the nuclear walls, that is, actual fusion, is for some time delayed. After fusion has taken place, but while the outlines of the two nuclei are still distinct, the chromosomes can be distinguished as two separate groups derived from the male and female nuclei respectively. Indications of the first segmentation spindle are also to be observed at this stage as fine staining threads running throughout both nuclei. No definite resting fertilised nucleus is formed. The spindle, which lies obliquely in the centre of the egg, is at first multipolar in form, and while it is in this condition the chromosomes begin to split longitudinally, but can still be distinguished roughly into two groups. Only after the formation of four segmentation nuclei do these begin to wander down to the base of the egg. On its way down each nucleus has a distinct sheath of cytoplasmic fibres, but when it reaches the base these become replaced by fine cytoplasmic threads, which run from the nucleus out into the general cytoplasm. These later-formed cytoplasmic threads seem to be connected with the formation of cell walls around the nuclei. The number of chromosomes in the egg nucleus was determined by counting them in the division which cuts off the ventral canal cell, and was found to be twelve. The same number was also to be found in the nuclei of the cells of the prothallial tissue and of the pollen mother cells. The chromosomes of the first segmentation spindle, on the one occasion on which they could be counted, were exactly twenty-four in number. The chromosomes were also counted in several types of sporophytic tissue; at least twenty-one chromosomes could always be observed; presumably twenty-four are always present. No centrospheres or centrosomes were to be seen in connection either with fertilisation or with any of the related processes. 66 Experiments on Aneroid Barometers at Kew Observatory and their Discussion." By C. CHREE, Sc.D., LL.D., F.R.S., Superintendent. Received May 5,-Read June 9, 1898. (Communicated by the Author at the request of the Kew Observatory Committee.) (Abstract.) The paper deals with two species of data. The first consists of particulars derived from the records at Kew Observatory as to the errors observed in about 300 aneroid barometers. These had been subjected to the ordinary Kew test, which consists in lowering the pressure to which the aneroid is exposed inch by inch to the lowest point at which verification is desired, and raising the pressure in a corresponding way to its original value. Readings are taken at each inch of pressure during both the fall and the recovery, and a table of corrections is obtained by reference to the corresponding readings of a mercury gauge. The second group of data are the results of special experiments made at Kew Observatory during the last three years. These were intended to link together the phenomena exhibited in the Kew verifications, and to further investigate various points bearing on the usefulness of the certificate hitherto issued to aneroids. The aneroid is an instrument exhibiting elastic after-effect, frequently in a conspicuous way. When pressure is lowered and then maintained constant, the aneroid's reading continues to fall, and when pressure is restored to its original value, the aneroid reads at first lower than it did originally, but exhibits a gradual tendency to recover. These general facts have of course been long known. The most characteristic features were in fact discussed 30 years ago by Dr. Balfour Stewart, then superintendent of Kew Observatory, who dealt with a considerable mass of experimental material. They have also been the subject of a comparatively recent pamphlet by Mr. Edward Whymper, who gives the results of a number of interesting long period experiments. pressure The present paper is partly experimental and partly theoretical. It treats of how the differences between the readings with pressure descending and ascending in a normal pressure cycle, such as the Kew test, vary throughout the range, and how the sum of these differences varies from one range to another. It investigates how the error, as pressure is reduced, varies with the rate of fall of (when uniform), how the fall of reading at a low stationary pressure increases with the time, depends on the pressure, and varies with the rate of the previous fall of pressure, and how the recovery after a pressure cycle progresses with the time, and is modified by the nature of the previous pressure changes. The influence of subsidiary stoppages during the fall or rise of pressure is investigated, and experiments are discussed showing the influence of temperature on the various phenomena. Some of the aneroids employed for the special experiments having been under observation for nearly three years, the opportunity is taken of considering the secular change of zero, and also changes in the elastic and the after-effect properties. Algebraic and exponential formulæ are obtained by trial for such phenomena as the variation of the differences of the descending and ascending readings throughout a pressure cycle, the dependence of the sum of such differences on the range, the fall of reading at the lowest pressure and the final recovery. A theory, to some extent empirical, is built up, leading to mathematical results, depending on only three arbitrary constants, for the behaviour of an aneroid in the ordinary Kew test over any range. One of these constants varies with the aneroid, but is determined by the observed value of such a quantity as the sum of the differences of the descending and ascending |