February 2, 1893] 



NATURE 



3«9 



Observatory party, which is to occupy a station in Chili, 

 but Prof. W. H. Pickering writes that difficulties of 

 transport will prevent him from taking the 20-inch mirror 

 he has at Arequipa to the Harvard station ; and owing to 

 this and to the already large programme of the English 

 party in Africa there is some doubt whether they will 

 take one of the mirrors. April being the middle of the 

 rainy season in Brazil, it is not deemed advisable to send 

 one of the mirrors to that station. 



The duration of totality at Para Cura is four minutes 

 forty-four seconds, the altitude of the sun being between 

 70' and 80°. At Fundium the totality lasts four minutes 

 eight seconds, the altitude of the sun being about 54°. 



The Joint Eclipse Committee having arranged the 

 expeditions and the general scheme of work, final details 

 as to the actual operations have been left to a sub-com- 

 mittee consisting of the Astronomer Royal, Captain 

 Abney, Mr. H. H.Turner, Prof. Thorpe, Mr. A.Taylor, and 

 the secretary, Dr. Common. Prof. Lockyer, previous to 

 leaving England for Egypt, determined the exposures 

 to be given by Messrs. Fowler and Shackleton with the 

 integrating spectroscopes. These, with the final instruc- 

 tions to observers drafted by the sub-committee, will be 

 published in due course. 



At present very few details are available as to the 

 actual work to be undertaken by foreign observers. The 

 Harvard College Observatory expedition to Chili has 

 already been mentioned. Prof. Schaeberle, of the Lick 

 Observatory, has already started for Chili, and will use a 

 six-and-a-half-inch equatorial, a five-inch horizontal 

 photoheliograph of forty-feet focus, and a Uallmeyer 

 portrait lens. He will be assisted by Mr. Gale, an 

 amateur, from Paddington, N.S.W. A Chilian party will 

 also observe the eclipse in Chili. 



At Para Cura there will probably be two or three 

 American parties, one being announced as probably under 

 Prof. H. S. Pritchett, from Washington University, St. 

 Louis, and another will probably be brought to that 

 station by Prof. David P. Todd. A Brazilian party will 

 also observe. The Bureau des Longitudes, Paris, are 

 sending a complete expedition to Joal, in Africa, under 

 MM. Deslandres and Bigourdan, the latter observer 

 having already started for his station. The work under- 

 taken will be to obtain photographs of the corona and of 

 its spectrum. M. de la Baume Pluvinel will also go to 

 Joal to photograph the corona. At present we have not 

 heard of any Italian expedition, but it is hoped that Prof. 

 Tacchini will be able to arrange to observe the eclipse. 



A. Taylor. 



MEASURE OF THE IMAGINATION} 



T^HE first perceptible sensation is seldom due to a 

 -*• solitary stimulus. Internal causes of stimulation 

 are in continual activity, whose effects are usually too 

 faint to be perceived by themselves, but they may combine 

 with minute external stimuli, and so produce a sensation 

 which neither of them could have done singly. I 

 desire now to draw attention to another concurring cause 

 which has hitherto been unduly overlooked, or only 

 partially allowed for under the titles of expectation and 

 attention. I mean the Imagination, believing that it 

 should be frankly recognised as a frequent factor in the 

 production of a Just perceptible sensation. Let us reflect 

 for a moment on the frequency with which the im- 

 agination produces effects that actually overpass the 

 threshold of consciousness, and give rise to what is indis- 

 tinguishable from, and mistaken for a real sensation. 

 Every one has observed instances of it in his own person 



' Extract from ft lecture on " The Just-Perceptible Difference," delivered 

 before the Royal Institution, on Friday, January 27, by Francis Gallon, 

 F.R.S. We hope to give next week an extract on "Optical Continuity." 



NO. I 2 14, VOL. 47] 



and in those of others. Illustrations are almost needless ; 

 I may, however, mention one as a reminder ; it was cur- 

 rent in my boyhood, and the incident probably took place 

 not many yards from where I now stand. Sir Humphrey 

 Davy had recently discovered the metal potassium, and 

 showed specimens of it to the greedy gaze of a philoso- 

 phical friend as it lay immersed in a dish of alcohol to 

 shield it from the air, explaining its chemical claim to be 

 considered a metal. All the known metals at that time 

 were of such high specific gravity that weight was com- 

 monly considered to be a peculiar characteristic of metals ; 

 potassium, however, is lighter than water. The philoso- 

 pher not being aware of this, but convinced as to its 

 metallic nature by the reasoning of Sir Humphrey, fished 

 a piece out of the alcohol, and, weighing it a while be- 

 tween his finger and thumb, said seriously, as in further 

 confirmation, " How heavy it is ! " 



In childhood the imagination is peculiarly vivid and 

 notoriously leads to mistakes, but the discipline of after 

 life is steadily directed to checking its vagaries and to 

 establishing a clear distinction between fancy and fact. 

 Nevertheless, the force of the imagination may endure 

 with extraordinary power and be cherished by persons of 

 poetic temperament, on which point the experiences of 

 our two latest Poet-Laureats, Wordsworth and Tenny- 

 son, is extremely instructive. Wordsworth's famous 

 " Ode to Immortality " contains three lines which long 

 puzzled his readers. They occur after his grand de- 

 scription of the glorious imagery of childhood, and the 

 " perpetual benediction " of its memories, when he 

 suddenly breaks off into — 



" Not for these I raise 

 The song of thanks and praise, 

 But for those obstinate questionings 

 Of sense and outward things, 

 Fallings, from us, vanishings," &c. 



Why, it was asked, should any sane person be " ob- 

 stinately" disposed to question the testimony of his 

 senses, and be peculiarly thankful that he had the power 

 to do so ? What was meant by the " fallings off and 

 vanishings," for which he raises his " song of thanks and 

 praise " 1 The explanation is now to be found in a note 

 by Wordsworth himself, prefixed to the ode in 

 Knight's edition. Wordsworth there writes — " I 

 was often unable to think of external things as 

 having external existence, and I communed with all I 

 saw as something not apart from, but inherent in, my 

 own immaterial nature. Many times while going to 

 school have I grasped at a wall or tree to recal myself 

 from this abyss of idealism to the reality. At that time 

 I was afraid of such processes. In later times I have 

 deplored, as we all have reason to do, a subjugation of 

 an opposite character, and have rejoiced over the remem- 

 brances, as is expressed in the lines ' Obstinate question- 

 ings,' &c." He then gives those I have just quoted. 



It is a remarkable coincidence that a closely similar 

 idea is found in the verses of the successor of Words- 

 worth, namely, the great poet whose recent loss is 

 mourned by all English-speaking nations, and that a 

 closely similar explanation exists with respect to them. 

 For in Lord Tennyson's " Holy Grail " the aged Sir 

 Percivale, then a monk, recounts to a brother monk the 

 following words of King Arthur : — 



'* Let visions of the night or of the day 

 Come, as they will ; and many a time they come 

 Until this earth he walks on seems not earth, 

 This light that strikes his eyeball is not light, 

 The air that smites his forehead is not air, 

 But vision," &c. 



Sir Percivale concludes just as Wordsworth's admirers 

 formerly had done : " I knew not all he meant" 



Now, in the Nineteenth Century of the present month 



' Knight's edition of Wordsworth, vol. iv. p. 47. 



