Atig. 8, 1872] 



NATURE 



293 



A suri'LEMENT to the fifth annual report of the United States' 

 Geological Survey has just been published. It consists of an 

 enumeration, with descriptions by M. Lesquercux, of tertiary 

 fossil plants collected by Dr. F. V. Hayden in 1S70, from which 

 some important climatic and other conclusions are dra«n. 



It is stated that a plan has been submitted to the Spanish 

 Ciovernment for a tunnel under the Straits of Gibraltar, which 

 might be connected with the shortest route to India. The IenL;lh 

 to be traversed would be 13,800 metres, while that of the con- 

 templated Dover and Calais tunnel is stated as 32,000. 



The late thunderstorms have done considerable damage to the 

 Postal Telegraphs of the United Kingdom. Demagnetisation of 

 nceilles, and in a large number of instances the fusing and com- 

 jjlete destructions of the instrument coils, show that the want of 

 an efficient lightning piotector is still much felt. 



Cork trees are being extensively introduced into Southern 

 California. 



FORMS OF SOLAR PROTUBERANCES* 



PROFESSOR TACCHINI gave a full .iccount of some of 

 -^ the work recently done by the Italian Society of Spectro- 

 scopibts, which will be read with interest. At the beginning of 

 his discourse he dealt specially with the observations on the solar 

 protuberances, made with the view of throwing light on tlie ques- 

 tion, whether the strata below the sun's chromosphere are solid, 

 liquici, or gaseous. If we suppose that the protuberances have 

 the form of jets, that is to say, narrow at the base and spreading 

 out like a fan, as in the jets of gas whicli issue from terrestrial 

 volcanoes, and if, moreover, instead of being composed of one 

 element or a small number of elements, tliey are composed, from 

 base to summit, of numerous materials, then it will appear 

 probable that they are produced by eruptions taking place through 

 a strongly resisting medium ; and consequently that there must 

 be ah-eady formed, on the surface of the sun, a crust solid enougli 

 to resist, for the most part, the powerful tension of the internal 

 incandescent gases, which, breaking through this crust at certain 

 points, give rise to violent ei-uptions, constituting the phenomenon 

 of the solar protuberances. On the other hand, if all or most 

 of the protuberances have a wide base and taper upwards like a 

 pyramid, if their composition is simple, perhaps of the same 

 materials as the chromosphere — a complex composition occurring 

 only in a few of them, and at the base or at a small height above 

 it — then the protuberances, properly so called, must be regarded, 

 not as true eruptions, but as alterations of the chromosphere in 

 those parts, where, through special circumstances, the composi- 

 tion of the subjacent strata becomes modified, either by an out- 

 flow of the internal constituents of the solar sphere — in which 

 case the phenomenon is brought about by internal causes— or by 

 disturbances arising in ])articular zones in consequence of move- 

 ments developed in the sun's atmosphere, in which case the pro- 

 tuberances are produced by external causes ; in other cases both 

 these causes may concur in the production of the phenomena 

 • <i question. 



These considerations are sufficient to show the great import- 

 ance of establishing the general character of the solar protuber- 

 ances, and for this purpose, and to avoid certain sources of error, 

 I'Jof. Tacchini invited P. Secchi, at Rome, and Prof. Lorenzoni, 

 at Padua, to join with him in making contemporaneous obser- 

 vations of the solar protuberances. The proposal was favourably 

 received, and it was agreed that from the 1st to the 13th of July, 

 1S71, observations of the entire limb of the sun should be made 

 from 7 lo 10 o'clock. 



The spectroscope employed by Tacchini at Palermo is formed 

 of three direct vision prisms, constructed by Tauber, of 

 Leipzig ; that of P. Secchi is an instrument with angular vision, 

 somewhat inferior in power to the Palermo instrument ; and th.at 

 of Prof. Lorenzoni is a direct-vision spectroscope which was used 

 in Sicily in the observation of the total eclipse of 1870. 



A comparison of the observations made at Rome and at 

 Palermo led to the following results : — 



I . All the masses are found indiscriminately in the drawings 



* " On tlic Forms of the Solar Protuberances and the Regions of Mag- 

 nesium and Iron on the Surface of the Sun." By P. Tacchini (Public Con- 

 ference held on Feb. 18, 1872, in the Royal University of Palermo). 



made at Rome and at Palermo ; the most remarkable peculiarities 

 of the chromosphere are likewise reproduced in both. 



2. The principal ch.aracters of the forms of the protuberances are 

 identical in the two sets of drawings ; the direction and position 

 of the plumes, the luminous masses, and frequently the regions 

 of the chromosphere where the flames have a peculiar appear- 

 ance, are perfectly identical. 



3. The heights of the protuberances are for the most part the 

 same, notwithstanding the diversity of the methods employed for 

 measuring them. 



4. The differences in the two sets of delineations are of two 

 kinds : the first arising from the mode of drawing, the second 

 from the greater distinctness of vision at Palermo. Other 

 differences are real, being due to the rapid changes taking place 

 in the protuberances. 



At Padua the observations were limited to the delineation of 

 individual protuberances ; these were found to be the same in form 

 and altitude as those seen at Rome and Palermo, thus affording 

 proof that at the three stations, with different means of observa- 

 tion, the objects seen were identical, and removing .any doubt 

 that might previously have existed as to the power of the spectro- 

 scope to afford accurate results respecting the chromosphere and 

 the forms of the protuberances. 



Tacchini next proceeded to consider the general form of the 

 protuberances. By observations with the spectroscope, con- 

 tinued from March 1S71 to Febriiai-y 1872, he found that out 

 of 2,903 protuberances, only 234, or abour 8 per cent, have 

 the form of a tree or of a fan, that is to say, are narrow at the 

 base and spread out towards the upper part, as if they were 

 produced by volcanic eruptions, whereas the remaining 92 

 per cent, have a broad base and taper upwards like a pyramid, 

 seem, therefore, to be due rather to a simple throwing up of 

 the substance of the chromosphere. He, therefore, regards the 

 general form of the protuberances as inconsistent with the exist- 

 ence of a solid crust on the surface of the sun. This is entirely 

 in accordance with the English work. 



When the chromosphere is observed with large instruments — 

 and under peculiarly favourable conditions — it does not present 

 the appearance of a continuous level stratum, as should 

 be the case if it were solid, pasty, or liquid, but often ap- 

 pears to be formed of a continuous series of very distinct flames.* 

 It looks indeed like a general conllagralion, more or less de- 

 veloped, which is incessantly renewed with greater or less force, 

 and with especial violence in particular parts, where it gives rise 

 to the protuberances. In small instruments, on the contrary, the 

 chromosphere appears smooth, excepting certain parts where the 

 flames rise to an unusual height. In like manner the details of 

 the protuberances, and especially their outlines, as observed with 

 small instruments, are not comparable with those made with 

 large telescopes, which must necessarily afford a higher degree of 

 definition. 



Tacchini next described certain observations which tend to 

 show that the so-called jets, projected upwards from the chromo- 

 sphere, have their counterpart in a descent of matter from above, 

 in a kind of solar i-ain, when a mass or cloud of luminous hydro- 

 gen suspended in the ,sun's atmosphere throws off filaments on 

 both sides, which gradually descend and unite at the sun's edge, 

 thereby forming a protuberance which exhibits the arborescent 

 or fan-like form usually attributed to an eruptive jet. This is a 

 new point of great interest. 



The theory which attributes the solar protuberances to violent 

 eruptions forcing their way through a solid crust, or a liquid of 

 great resisting power, may, Tacchini remarks, appear to derive 

 some support from the chemical composition of the protuberances. 

 If the masses which project above the chromosphere were found 

 to contain many materials different from those which compose 

 the chromosphere itself, there would be good reason for regard- 

 ing them as projected from the interior of the sun. And, in fact, 

 some of the protuberances have a somewhat complex chemical 

 composition, the bright lines observed in their spectra often cor- 

 responding to m.igne5ium, iron, sodium, titanium, calcium, 

 barium, nickel, chromium, copper, together with eight other lines 

 which may belong to as many different substances ; in all there- 

 fore eighteen elements, besides hydrogen and the element provi- 

 sionally named Helium, which is never absent, and represents the 

 constant material of the entire chromosphere. On August 27 

 last in a single protuberance nine different substances, represented 

 by a brilliant spectrum of twenty-four bright lines, nine of which 

 belonged to iron were seen. 



^ See Lockyer, Proc. K. S. vol. xvii. 1870, p. 354. 



