88 



NATURE 



{7nne s, 1875 



General Catalogue," two authorities supplying him with 

 excellent positions of a large number of stars. 



The Comet of 1533. — In the catalogues of the orbits 

 of comets we find two sets of elements for this comet, 

 both deduced from the observations of Apian between 

 July 18 and 25, which are contained in his rare work, 

 Astrononiiann Casareiim. The first orbit is by Douwes, 

 who assigned reti-ograde motion, but in the Berliner 

 Jahrbnch for 1800, Olbers gives another orbit, equally 

 satisfactory as regards representing Apian's observations, 

 in which the heliocentric motion is direct^ and he appeared 

 to think it was not possible to decide which of the two is 

 to be preferred. In addition to Apian's account of this 

 comet we have a brief one by Gemma Frisius, who states 

 that after having been seen about the beginning of July 

 in 5° (or rather, as Pingr^ corrects him, in 15°) of the sign 

 Gemini, near the star Capella, with 24° of latitude and 48° 

 north declination, it passed by a westerly motion, or con- 

 trary to the order of the signs, to the constellation Cas- 

 siopea, which it traversed, finally disappearing in Cygnus. 

 Fracastor has also left us an account of the comet's track, 

 though there is some ambiguity about it. Since Olbers 

 calculated the orbit the Chinese observations have been 

 published, in the first instance by M. Edouard Biot, in 

 the additions to the Connaissance des Tevips for 1 846, 

 and more recently in Mi\ Williams' work upon Cometary 

 Observations in China, and it would appear that the 

 comet moved to the vicinity of tt Cygni, and was last seen 

 on .Sept. 16. If we compare the elements of Douwes and 

 Olbers with the track thus roughly defined, we see that 

 the retrograde orbit of Douwes is hardly probable, and 

 that possibly a modification of the direct orbit of Olbers 

 would be found to sufficiently represent the path of the 

 comet, according to Apian, Gemma, and the Chinese 

 Annals. 



Occult ATiON of Venus.— Mr. R, Meldola, of the 

 Royal Society Eclipse Expedition, writes that the occul- 

 tation of May 2 was partially observed by Prof. Tacchini 

 and himself from the P. and O. steamer Pcshawnr in the 

 Arabian Sea. The moon was obscured by clouds at 

 the time of immersion ; the last contact took place at 

 i6h. 15m. 6s. local mean time. Ship's position furnished 

 by Capt. White— long, ^f 3' E., lat. 6° 48' 18'' N. 



OUR BOTANICAL COLUMN 

 Phenomena of Plant-life. — The expansive power 

 of growing vegetable tissue is something marvellous, 

 if the experiments undertaken by Mr. Clark, pre- 

 sident of the State Agricultural College of Massa- 

 chusetts, are perfectly trustworthy. If his appliance 

 for measuring the force exerted by a growing pumpkin 

 was not at fault, the greatest weight lifted by the 

 pumpkin in the course of its development was nearly 

 two-and-a-half tons. Apparently the greatest care 

 was taken to arrive at the truth, and we have no 

 reason to doubt the accuracy of the statements con- 

 tained in Mr. Clark's paper which was presented to 

 the Massachusetts Board of Agriculture. But in our 

 ignorance of the phenomena of plant life we should 

 like to see the observations repeated. At the end of 

 the experiment alluded to the soil was carefully washed 

 from the roots of the pumpkin vine, and the entire system 

 of roots spread out upon the floor of a large room and 

 carefully measured. In addition to the main root, roots 

 were formed at each joint or node. The total length of 

 root developed was calculated to be over fifteen miles ; 

 and the time the plant was growing, four months. During 

 the greater part of the time, of course, the rate of growth 

 was relatively slow, but the maximum rate was computed 

 at not less than one thousand feet of root per day. 



With another plant of the same species, Cticurbita 

 maxima, an experiment was instituted to ascertain the 

 pressure exerted by the rising sap. For this purpose the 

 plant was cut off near the ground, after it had attained 



a length of twelve feet, and a mercurial gauge attached 

 to the part left in the ground. The maximum force with 

 which the root of the pumpkin exuded the water absorbed 

 by it was equal to a column of water 48"5i feet in height. 



Some experiments to determine the channels through 

 which the crude sap rises, and on the diffusion of the 

 elaborated sap, gave interesting results. Mr. Clark says : 

 " We find that the crude sap imbibed by the root-hairs 

 from the surface of the particles of the soil seems to be 

 taken up in a dry state ; that is, it appears to be absorbed 

 molecule by molecule, no fluid water being visible, and 

 carried in this form through all the cellulose membranes 

 between the earth and leaf, by which it is to be digested 

 or exhaled. We do not say this is literally true, but it 

 accords very nearly with what is constantly to be seen in 

 some species of plants. The circulation of the sap in a 

 poplar tree is very dry compared with that of the blood 

 of any animal. Not a drop of moisture will ever flow 

 from the wood of an aspen, so far as we have observed." 

 It was found that an exceedingly small proportion of sap- 

 wood sufficed to convey the necessary supply of crude 

 sap to the foliage, but none would ascend through the bark. 



The quantity of sap that flowed from difterent trees 

 during the season varied greatly in diverse species. Thus 

 the entire flow from the bitter-nut was less than the pro- 

 duct of the sugar-maple for a single day ; but the iron- 

 wood and the birches surpass the maple in the rapidity 

 and amount of their flowing. A paper-birch, fifteen inches 

 in diameter, bled in less than two months over one thou- 

 sand four hundred and eighty-six pounds of sap ; the 

 maximum flow, on the 5th of May, amounting to sixty- 

 three pounds and four ounces. The grape bleeds compara- 

 tively little as compared with many other things. A very 

 large proportion of the trees experimented upon did not 

 show any tendency to bleed in spring. We might extract 

 many other interesting details from Mr. Clark's paper, 

 had we sufficient space for them. 



PHYSICS IN GERMANY 

 {Ftotn a German Correspondent^ 

 TT ERR STEFAN, of Vienna, hss pubhshed a paper on 

 ■»■-*■ a series of researches on adhesion. It is well known 

 that two plane plates which are placed upon one another ad- 

 here together so firmly that they can only be separated by a 

 certain amount of force. This phenomenon has hitherto 

 been considered as caused by adhesion {i.e. by the action 

 of molecular forces between the particles in contact be- 

 tween the two plates), and it was tried to determine the 

 magnitude of this adhesion statically. 



The improbability of this conception already follows 

 from the fact that in the case in question no immediate 

 contact of the two plates takes place, but that between 

 them there is a layer of air of considerable thickness. If 

 two glass plates are employed for this experiment, they 

 do not show Newton's coloured rings ; these can only be 

 produced with plates that are perfectly plane and with the 

 application of considerable pressure. If, therefore, mole- 

 cular forces were active in this case between the particles 

 of the two plates, then the molecular sphere of action 

 would have to be very much larger than is generally 

 adopted according to other experiments. The phenome- 

 non becomes still more striking if the experiment is made 

 under water. In that case an attraction in the two plates 

 can still be perceived, even if they are a millimetre apart. 

 Herr Stefan used for his experiments two plates of glass, 

 of which one was suspended from a balance in such 

 a manner that its inferior plane was horizontal. The 

 balance was then brought to equilibrium. The second 

 plate was also placed horizontally under the other one. 

 Three little pieces of wire were then placed upon it, and 

 the upper plate was then let down so far as to rest upon 

 these pieces of wire. By varying the thicknesses of the 

 wires the distance of the two plates could be brought to 

 any desired magnitude. To tear away the upper plate 



