Oct 17, 1878] 



NATURE 



643 



■ Several small hunting spiders are to be found in the wasps 

 nests -which do not seem to leave any line behind tliem, and 

 whose mode of life is very nomadic. I quite believe from obser- 

 vation that wasps can and do run these insects down by scent, 

 although it is difficult to obtain direct proof of the fact. They 

 seem quite capable of discerning between their prey and enemies, 

 as shown above ; and granting this, it does not seem a great 

 stretch to a further development of instinct having the propaga- 

 tion of the species in view. 



Can any of yoin: readers explain to me in what manner the 

 spiders are stupefied and not killed ? 



I have lately noticed cases of protective mimicry in birds 

 which I think are worth recording. 



While following a small wood- swallow (Artatnus minor) a 

 few evenings back, they suddenly disappeared near a large leaning 

 gum-tree. Walking up to the spot they suddenly flew out of 

 the trunk, which I found had been hollowed out by fire, leaving 

 the inside charred and black. The birds had chosen this black 

 surface as their roost, and when followed in the day-time 

 invariably flew into this refuge. It was impossible to detect the 

 birds when clinging to the charred surface, with which their 

 plumage matched. t':?rj 



Artamus albizxntris, I find, in like manner chooses a greyish 

 back as a roost against which they are less liable to be detected. 

 Eryihiina vespertilio is a favourite tree with this species. 



I have on several occasions taken Podargus gigantats and 

 other species alive by hand in broad daylight. These birds sit 

 perfectly still on a limb of an iron-bark or acacia, whose 

 bark resembles their plumage in colour. W. E, Armit 



Georgetown, Queensland, July 19 



Agricultural Ants 



I HAVE lately discovered a colony of agricultural ants near 

 Georgetown. The species is very small and red. 



My attention was first directed to these tiny harvesters by 

 noticing heaps of chaff and hulls in a bare spot situated in a 

 grove of young acacia trees. 



The formicaries are entirely subten-anean, being entered by a 

 funnel-shaped tube. 



Roads diverge from this gate in foxir or five directions, and 

 during working hours are alive with what appear like white 

 insects, the little ants being covered by their load. Some of 

 these ants seem to clean the grain and carry ouc the husks, 

 which form a heap round the opening to the nest. The clear 

 space round each opening is small, certainly not more than 

 eighteen inches in circumference, and a small mound not 

 more than six inches in height is formed with the earth exca- 

 vated in forming the nest. The only species of grain har- 

 vested is the seed of Perotis vara, whch is light when quite ripe. 

 I cannot give the generic name of these little fellows, never 

 having devoted any special study to the family, but shall be happy 

 to furnish specimens in spirits to any naturalist who will forward 

 his address, William E. Armit 



Dunrobin, Georgetown, July 19 



Meteor 



At about 5.50 p.m. to-day I saw a most brilliant meteor fall 

 quite close to the moon, which was shining brightly at the time : 

 it was in full daylight, shortly after the sun had gone down. 

 Its direction was nearly perpendicular, but inclined a little from 

 north to south as it fell. It was of a bright gi"een colour ; its 

 motion rapid, its path long, and the time during which it was 

 visible about two seconds, and it left no visible trace behind it. 



Harlton, Cambridge, October 8 O. P, Fisher 



JANSSEN'S NEW METHOD OF SOLAR 

 PHOTOGRAPHY 



IN two papers published respectively in the Comptes 

 Rendiis for December, 1877, and in the Anmiairt 

 of the Bureau des Longitudes for the current year, M, 

 Janssen has described a new method of photographing 

 the solar disc, which he has successfully carried out at 

 the Meudon Observatory, during the past twelve months ; 

 and he has also drav.'n attention to some striking features 

 in the constitution of the photosphere, disclosed for the 



first time in the beautiful pictures which are among the 

 first results of his process. These may be regarded as 

 only the forerunners of further important discoveries. 

 Through the courteous liberality of M. Janssen, I have 

 lately had the advantage of stud} ing the process in the 

 Meudon Observatorj', and a description of its distinctive 

 features, and a brief notice of such of the results as M, 

 Janssen has already published, will certainly be accep- 

 table to many who are interested in the recent develop- 

 ments of solar physics, and have not ready access to the 

 original papers. ' 



M. Janssen' s pictures of the solar disc are distin- 

 guished from all those previously obtained with the 

 photoheliograph, not only by their great size (30*5 ctm, 

 diameter), but more especially by the remarkable sharp- 

 ness and definition with which they display the details of 

 photospheric structure, which are such that, for the pur- 

 pose of their more effective study, it is found advanta- 

 geous to enlarge the Original pictures to three and even 

 nine times their original linear dimensions. The greatly 

 extended means of research which M, Janssen' s inven- 

 tion places in the hands of the solar physicist will te 

 obvious, when we consider the difficulties which attend 

 any prolonged ocular inspection of the solar disc, hitherto 

 the only practicable method of examining its detailed 

 structure. " In spite of the interposition of coloured 

 glasses, helioscopes, &c., the eye must seize on the de- 

 tails in a dazzling field, and perform its functions under 

 conditions which are quite unfamiliar. The true varia- 

 tions of luminous intensity in different parts of the image 

 can no longer be appreciated, and the impressions pro- 

 duced do not correspond to reality. Thus may be ex- 

 plained the diversity of the opinions which have been 

 put forward respecting the forms and dimensions of the 

 granulations, and of the constituent parts of the solar 

 surface" — diversities well illustrated by the old contro- 

 versy of the "willow-leaf" and "rice-grain" bodies in 

 the photosphere. In M. Janssen' s pictures the forms, 

 sizes, and arrangement of the bodies described under 

 these appellations are exhibited in the most satisfactory 

 manner, and as, in a favourable state of the atmosphere, 

 the pictures may be repeated at as short intervals as the 

 operator pleases, the movements and changes of form 

 exhibited by these bodies may be studied with the utmost 

 ease in a register which preserves the most fugitive 

 phases of their appearance, and is available for leisurely 

 re-examination at any future time. 



Before noticing the novel facts which M, Janssen has 

 thus brought to light, I will briefly describe the principles 

 of the process itself. The main difficulty to be sur- 

 mounted in order to obtain a sharply defined photo- 

 graphic picture of the details of the solar disc is presented 

 by the phenomenon known as photographic irradiation, 

 in virtue of which a brilliantly illuminated surface occu- 

 pies, on the negative picture, a proportionally exaggerated 

 space ; its borders being extended over the darker objects 

 around. This phenomenon, M. Janssen remarks, "is 

 very striking in all the photographs of total eclipses 

 which have been obtained since i860, which exhibit the 

 images of the protuberances encroaching on the lunar 

 disc, to the extent, in some cases, of ten and twenty 

 seconds of arc, and even more." The granulations (to 

 employ M. Janssen' s terminology) visible on the solar 

 disc have a mean diameter of not more than one second 

 of arc, and in ordinary photoheliograms their very exist- 

 ence is therefore completely masked by irradiation. 



' The present notice contains a mere detailed descripticn of the process 

 than M. Janssen's original papers, and is published with his full approval 

 and authority. With characteristic liberahty M. Janssen writes :— " Quant 

 au precede lui-meme, il est evident que toute perscnne un peu au courantde 

 la photcgraphie aftronomique pourra I'appliquer et obtenirbientot des photo- 

 graphies semblables a celles que ncus obtep.ons. Je serai aussi tres pro- 

 bablement devance sur plusieurs points de la ccnstltuticn du soleil que ces 

 pre ce'des peuvent reveler. L'inccnvenient n'est que pour mci, et je crois 

 qu'il vaut mieux des aujourd'hui livrer la methcde au public scientifique. 

 Les rrogrcs de la Ecier.ce y gagnercnt certainemert." 



