Oct. 13, 1S81] 



NATURE 



573 



earth's ?urface the atmospheric rarefaction mu^t be such as to 

 convert what would be lightning at a lower leve into a discharge 

 similar in the main to that in a vacuum tube. 



Further, it is an ascertained fact that a diilerence of electric-il 

 condition in different portions of the atmosphere often prevails. 

 We have, thereft're, not unfrequently pre^ent in regions at 

 moderate elevation>!, say from twenty to iifty miles, all the con- 

 ditions necessary fnr the production of an auroral display. 



-.'^nd nut only so, liut our experiments enable us to determine, 

 at all events approximately, some limits of elevation within 

 which this phenomenon can occur, and thereby to check the 

 very divergent esti'iatcs of thofc who have observed it. Esti- 

 mates of the altitude at which the auroral discharge takes place 

 have been mide from simultaneous observations at different 

 points, and these have ranged up to fifty or sixty, and evei to 

 281 miles. But even the lowest of these appears to he im- 

 probable. The pressure at Mhich the resistance of air is least is 

 a little less than "4 of a millimetre of mercury ; and the corre- 

 sponding elevation is about thirty-eight miles. A vacuum tube 

 measured by hundred-thousandths of an atmosphere would 

 correspond to an elevation of a little more than eighty-one 

 miles. Through a hydroge 1 vacuum at this pressure Mr. De 

 La Rue failed to obtain a discharge with 11,000 cells; r nd he 

 adds that "it may be assumed that at this height the discharge 

 would be considerably less brilliant than at thirty-eight miles, 

 should such occur." 



It seems to be a well-ascertained fact that in high latitudes 

 there are fewer thunderstorms and more auroras than in lower 

 latitudes. This fact points to the conclusion that, after a disturb- 

 ance, the redi-trihution of atmospheric electricity is effected by 

 one process or by the other, according to, or rather in con- 

 sequence of, the meteorological differences betneen arctic, 

 temperate, and tropical regions. In ccilder regions, "here the 

 air is generally drier, and, consequently, a better insulator than 

 in warmer, there is less liability to a discharJe taking place in 

 the lower and denser strata ; that i*, there is less lialiility to 

 lightning. But at higher leveh the rai'efaction may compensate 

 this, and cause an auro al discharge to take place instead. 



There are other features in which a comparison may be made 

 between the auroral light and vacuum discharge . The>e dis- 

 cbarges, when free to arrange themselves in a magnetic field, 

 follow the lines of force ; the auroral streamers appear to run 

 parallel to the dipping needle. The colour of such discharges 

 varies n ith the exhaustion ; that of the aurora varies, like that of 

 an air-vacuum, from red almost to white ; and in the absence of 

 independent obyervations to the contrary, we may fairly attribute 

 the v.ariety of tint in the aurora partly to a diver-ityof elevation, 

 and, consequently, of rarefaction in the region where it takes 

 plrce, but partly also perhaps to the electrical conditions present 

 anterior to the passage of the di^chnrgf. 



These and other features of the phencmenon of the aurora, as 

 well as the kindred subjects of earlh cun-ents, the disturbances 

 of the magnetic needle, and the connection of the whole with 

 solar radiation as a predisposing cause, have been brought to- 

 gether under one theoretic view by Prof. Stokes, to whom I 

 am indebted for much of what I have here raid on the subject. 



Having thus gone through, so far as circumstanc:s permitted, 

 the experimental and inductive parts of my subject, it might 

 have been very pleasant to have cast aside for a few moments 

 the links which connect strict induction with what maybe termed 

 the fixed points of ascertained fact ; and, restrained only by the 

 more elastic bonds of scientific imagination, to have indulged in 

 speculations about things still lying on the borders of science 

 and of dreamland. But I must leave each of you to follow out 

 this vein of thought after your own fashion; ard, confininj 

 myself to a single remark, I will simply indicate the direction 

 in which my own thonghts on the present subject are ii^clined to 

 turn. The remark is this : If in the search for a solution of the 

 mystery of electricity there be one element more deserving our 

 attention rather than another, it is that of time. We haveutilisfd 

 this element in our experiments with the revolving mirror ; and 

 we have touched upon its more subtle influences in our conclu- 

 sions about the small time quantities in relation to the discharge. 



All operations of nature take place in time. It is in the time- 

 sequence of phases, often apparently simultaneous, but in reality 

 successive, that we m,ay hope to strike the origin of many com- 

 plicated phenomena. Time is the ocean beneath whose waves 

 and wh'-'se currents the secret fountains of truth are to be sought. 

 Time is the oce.an whose mighty stream encircles onr life. Time 

 is the ocean whose "countless smiles" jrave birth to Vennsand 



the Nei eids and all the infinite forms of beauty and of bright- 

 ness which play around our youth Time is the ocean from 

 whence sprang also the steeds of Neptune, typical of the strength 

 of our mo e mature years. Time is the ocean in whose loving 

 arms we fall .asleep, when the sun sinks low on the horizi.n, and 

 the shades of night are creeping over the heavens, and all things 

 tell us that our course is run. 



BIOLOGY AS AN ACADEMICAL STUVY^ 

 II. 



TT may help to the understanding of what I mean by a sound 

 method of biological teaching if I give a brief outline of the 

 course of study I hope to pursue with my students this session. 

 It is hardly necessary for me to state that this course is derived 

 from Prof. Huxley's by a natural procejs of descent with 

 modification. 



In the first place there will be some four or five lecture; on a 

 common flowering plant, giving an account of its ordinary 

 structure as seen by the naked eye, of its microscopic structure, 

 of its physioli gy, and of the process of its develipment. After 

 each lecture the students will examine for themselves the plant 

 described, learning not only to dissect it in the ordinary way, 

 but to make preparations for the microscope. By this means 

 they will be familiarised with the use of the microscope, the 

 emplujment of staining fluids, and other reagents ured in the 

 investigation of minu'e structure, and with the chief processes of 

 manii-ulation. As the laboratory will be 01 en for nine hours a 

 week, so as to give three hours for working out what has been 

 described in each hour's lecture, it is to be expected that a 

 student of average intelligence will, by the time this part of the 

 course is over, have a very fair notion of what a flowering 

 plant is, of the processes by which its life is carried on, and of 

 the manner in which it originates. 



The next few lectures, and the corresponding portion of the 

 practical course, will be occupied with a similar treatment of an 

 animal : the one selected, as on the whole the most convenient 

 and the most instructive, being the common sea crayfish of our 

 m.arkets. In the examination of this organism, the ^tudents 

 will learn something of the art of dissection, and will further 

 apjly the knowledge of microscopic structure which the study of 

 the plant has given them, to the far nu re difficult problems of 

 animal histology. The study of the crayfish, and the comparison 

 of it, point by point, with the plant, should give a clear concep- 

 tion of ihe main points of difference and of likeness between the 

 more highly organised animals and plants — between ania als and 

 plants as they are generally known to us. 



In dealing with these types in the lectures it will be my aim 

 always to proceed from the knov\n to the unknown; to begin 

 with points which every one who has seen a flowering plant or a 

 crayfish niu t have noticed, gradu.ally leading up to such points 

 of structure as require minute obsei-vation to verify them, and 

 above all never to give a definition or a general statement 

 without first supplying the facts from which it is legitimately 

 deducible. 



Next, 1 propose to take a number of types selected on the one 

 hand from the lowest plants, on the other from the lowest 

 animals : to show how these unicellular organisms agree in 

 structure and in the nature of their physiological processes with 

 the individual cells of which the bodies of the higher plants and 

 animals are made up, and to point out how, in de-din^ with 

 these lowest members of the two kingdoms of organic nature, 

 the boundaiy line between the two kingdoms tends to disappear, 

 and it becomes very difficult, sometimes even impossible, to say 

 nhat is a plant and what an animal. The study of these lowly 

 forms will also lead to the question of the origin of life, and it 

 will be necessary to say something of the attempts which have 

 been made to establish the doctrine of spontaneous generation, 

 and to discuss their value. 



The consideration of a few other animal and vegetable types, 

 especially such as, although multicellular, exhitit none of the 

 complex tissues found in the higher animals and plants, will 

 bring the introductory part of the course to a close — the part 

 which deals with the general facts and principles of biology. In 

 it the student should learn how animals and plants agree with 

 and differ from each other, and from inorganic bodies ; what are 

 the relations of animals and plants to one another, and to 



^ Inaugural Lecture delivered in the University Library, May 3. 1881, by 

 T. Jeffery Parker, B.Sc. Lond., Professor of Biology in the University of 

 Otago. Continued from p. 546. 



