September 21, 1905] 



NATURE 



5', 



nature-study affording- an unique opportunity for 

 heuristic teaching, the very complexity of the 

 problems which its subject-matter presents puts it at 

 a disadvantage as compared with the simpler problems 

 of elementary physics and chemistry. 



Again, how can we reconcile the foregoing quota- 

 tion with the following, which precedes it by a few 

 pages? 



" When a dog has been used as the subject of an 

 observation lesson, the children may read, or be told, about 

 the wolf or the fox. This will lead them to compare and 

 contrast, and will aid in stimulating imagination " (p. 46). 



Must we say that the dog is part of " nature " 

 while the wolf and fox are not? or that methods 

 bad for children over ten are allowable below that 

 age? or must we simply explain the difference as due 

 to composite authorship, permissible in a book of 

 suggestions (not instructions), coupled with some con- 

 fusion of mind on the part of one author between 

 method and subject-matter? 



The true idea of the relative positions which 

 heuristic and didactic methods should occupy, which 

 to our mind is well illustrated bv the above simple 

 case of the dog and the wolf, is clearly expressed in 

 the chapter on geography : — 



" In order that the study of geography may be of real 

 educational value it must not be regarded as a process 

 by which certain facts about the earth . . . are committed 

 to memory. It must be rather regarded as the subject, 

 which above all others brings the youngest child as well 

 as the most advanced student into contact with the outside 

 world. ... It is true that as we advance in the study 

 of geography we have to rely, to a great extent, upon the 

 investigations of others, but in order that they may under- 

 stand these investigations we must from the very first 

 teach children to work for themselves and to take nothing 

 for granted." 



Nevertheless, it is not suggested that early geo- 

 graphical teaching shall be purely heuristic. On the 

 contrary, the value of stories of strange and distant 

 countries is strongly urged. At first these are 

 scarcely differentiated from fairy-tales, but with each 

 succeeding year they become more exact, until they 

 at length pass into definite geographical teaching for 

 which an observational basis has meanwhile been 

 prepared. Here we see a development of the idea 

 of the relation between didactic and heuristic teach- 

 ing. It is useless and unnecessary to think, even as 

 a remote ideal, of the exclusion of the former; all 

 that is necessary is to prevent it from being more 

 precise in character than is justified by the stage 

 attained in the latter. 



History, in spite of authoritative opinion to the 

 contrary, we must regard as a science, but one in 

 which heuristic teaching is out of the question. Like 

 the one side of geographical teaching, it grows out 

 of fairy-tales, and there need be no scruple in telling 

 young children traditional stories that have not 

 survived modern critical research. But we are glad 

 to see that visits to local places of historical interest 

 are recommended, and that in one at least of the 

 schemes suggested in the appendix the syllabus for 

 the highest class includes " first notions on the 

 materials of history and the use of evidence." Un- 

 fortunately, very few teachers will have had any 

 opportunity of acquiring the necessary knowledge on 

 this subject. A book treating in a simple manner 

 of the materials of history — and by no means confined 

 to the documentary portion — is much to be desired. 



To sum up the ideas we have so far gathered, we 

 venture to think that in some future edition of these 

 " suggestions " the division into subjects will perhaps 

 be largely abandoned, and in its place we shall have 



NO. 1873, VOL. 72] 



a division by methods which will by no means 

 coincide with groups of the present subjects. Even 

 the official time-tables may come to recognise this. 

 On the one hand we shall have heuristic teaching,' 

 aiming primarily at training the mind in scientific 

 habits of thought, and incidentally imparting know- 

 ledge; on the other hand, didactic teaching to impart 

 knowledge which is wanted but cannot be obtained 

 at first-hand — its scope being carefully adapted to 

 the stage reached in heuristic training. But, along- 

 side of these two methods, there still remain a number 

 of other subjects, which do not fall under either of 

 these heads, since they consist in training or drilling 

 of some description, e.g. the use of the mother 

 tongue, singing, handiwork, and health-training. 

 This last, we agree with the writers of the Blue- 

 book, it is not advisable to teach to young children 

 on a physiological basis. Hygienic habits must be 

 learnt before the age at which physiological laws can 

 really be understood, since some knowledge of physics 

 and chemistry is essential to their real understand- 

 ing; and to attempt to teach them without such a 

 basis is only to give false knowledge, which is only 

 too likely to prevent the acquisition of true knowledge 

 in later years. A. M. D. 



A NEW ULTRA-VIOLET MERCURY LAMP. 



UNDER the name of "The Uviol Lamp," Dr. O. 

 Schott, of Jena, is introducing a modification 

 ot the Cooper Hewitt mercury vapour lamp, which 

 appears likely to prove useful. The illuminating 

 power of these lamps is very high, and the arc is very 

 rich in ultra-violet rays, but the glass envelope 

 hitherto prevented the passage of many of these 

 actinic radiations. Dr. Zchimmer has recently pro- 

 duced at Jena glasses which are pervious to the ultra- 

 violet rays, and Dr. Schott has made the envelope of 

 the new lamp of this material. 



The Uviol lamps consist of tubes of this special 

 glass of 8 to 30 millimetres diameter and 20 to 130 

 centimetres length. Platinum wires are fused into 

 the extremities, terminating in carbon heads. In the 

 glass tube there is a charge of mercury of 50 to 150 

 grs., according to the size. The lamps of various 

 sizes, with their resistance and choking coils, can be 

 connected with electric mains of 220 or 1 10 volts. 



To start the arc, the lamp is tilted to a sufficient 

 degree to allow of the mercury in the tube passing 

 from one pole to the other. At the moment of con- 

 tact between the pole and the mercury, part of the 

 latter is disintegrated simultaneously with the forma- 

 tion of a column of light. The carbon and heads to 

 the poles permit the p'assage of the current in either 

 direction without fusing the platinum poles. To get 

 the best results from a current of 220 volts the lamp 

 tube must be 130 centimetres long, but two or three 

 suitable shorter lamps may be arranged side by side 

 or one behind or over the other. 



The spectrum of the Uviol lamp is exceedingly rich 

 in lines. The lamp is particularly suitable for taking 

 photographs and for copying processes by artificial 

 light. Experiments have also been made in testing 

 by its means if certain colours used in dyeing and 

 printing have sufficient powder to resist the fading 

 effects of the sun. It will thus prove of value in 

 rapidly settling the question of the fastness of colours, 

 which will in future require days instead of months. 



The Uviol lamp is also a germicide, and it appears 

 likely that it will prove of value in the treatment of 

 certain diseases of the skin. It is an irritant, and 

 easily sets up inflammations, particularly of the eyes, 

 so that the greatest care must be taken by operators 



