9 8 



SCIENTIFIC NEWS. 



[Aug. 3, 1888. 



the horizon we are looking at him not merely through 

 the depth of our atmosphere, but also through a great 

 thickness in horizontal direction. 



The sun certainly has a great atmosphere of his own, 

 and if Spitta's results apply to self-luminous bodies as 

 well as to those illuminated by scattering reflection the 

 diminution of solar luminosity as we proceed from 

 centre to limb should be greater, not less, than in the 

 case of the plaster of Paris ball. 



Some experiments that I made about twenty years ago 

 supply a solution of this enigma. They were made with 

 the photometric apparatus of my old friend Mr. Jonathan 

 Wilkinson, the Official Gas Examiner to the Sheffield 

 Corporation, and with his valuable assistance. My object 

 was to learn whether a flame is transparent to its own 

 radiations, or, stated otherwise, whether a flame of given 

 intensity and exposing to the photometer a given area gives 

 out an increased quantity of light proportionate to increased 

 thickness or depth in the line of sight. Our experiments 

 were numerous, as the earlier experiments proved the 

 necessity of precautions that were not self-evident a 

 priori. Thus we found that two jets from the same-sized 

 holes, and each burning the same quantity of gas when 

 placed in contact one behind the other, gave more than 

 double the light of either, 2*15 times, and three jets gave 

 3 - 2, five jets gave 5-35, although the supply of gas was 

 regulated respectively to double, treble, and five times 

 the quantity supplied to the jets when burning singly. 



Without entering into further details (for which see 

 " The Fuel of the Sun," chapters vii. and viii.), I may 

 describe the most conclusive experiment which was made 

 with five simple round jets arranged in line about one 

 inch apart, and each with a separate tap. These were 

 adjusted to equal heights, and the row presented broad- 

 side to the photometer, so that all the jets were 

 separately radiating towards it. They were then turned 

 so that, instead of five jets being presented to the photo- 

 meter screen, only the end one was presented to it, and 

 thus the radiations from all the other four must pass 

 through this one. The photometer indicated no difference, 

 though in the first case five times the area of flame was 

 presented. The observer was so placed that he only saw 

 the disc of the photometer, the luminous object being 

 completely hidden from him. We turned the row of jets 

 round and round several times, changing places as observer 

 and manipulator, and could not tell which presentation, 

 whether broadside or endwise, was made ; our guesses, 

 based upon supposed increase of light, were as often 

 wrong as right. 



Similar experiments have since been made by others 

 who used fishtail and batswing burners, turning these 

 as we turned our row of equal jets. They found, as we 

 did in our preliminary experiments, that the edge 

 presentation of these gave less light than the broadside, 

 but failed to learn the reason. It is that such flames 

 have irregular summits, and that the edge view includes 

 something more than thickness of flame — viz., a thick- 

 ness of gas and vapour between the tips of the luminous 

 tail-summits through which the hinder tail summits must 

 radiate. It is well established that such vapours are 

 especially opaque to the radiations from the flame of 

 which they are the product. 



Applying this fact of free radiation of flame through 

 flame to the case of the sun, and assuming that the 

 photosphere of the sun consists of flaming matter of 

 considerable depth, we have in such depth a compensa- 

 ting factor to the varying depth of solar atmosphere 



presented to us. The visual depth of atmosphere and 

 the visual depth of flame will vary equally with the 

 different distances from the centre of the visual disc. 



I may add that the above-described experiments were 

 made in order to ascertain whether the great energy of 

 the solar radiations could be explained without recourse 

 to violent hypotheses concerning the temperature and 

 intrinsic luminosity of the solar material — without call- 

 ing upon the scientific imagination to create forms and 

 affections of matter different from those existing here on 

 our earth. 



THE FOURTH EXPEDITION OF THE 

 "HIRONDELLE": NEW DEVICES 

 FOR DEEP-SEA DREDGING. 



COME mention has already been made of the Hirondelle, 

 which under the command of the hereditary Prince 

 of Monaco, continues with success the explorations of the 

 Talisman and the Travailleitr. This vessel, admirably 

 equipped for a scientific cruise, has just sailed from 

 L'Orient for the Azores, in order to dredge at great 

 depths. The appliances for the expedition are numerous. 

 We must first mention the cable for lowering the other 

 apparatus to the bottom. It is more than 4,500 yards 

 in length, and is formed of six strands of steel wire, 

 forming a rope not so thick as a penholder, but capable 

 of bearing a strain of more than 2,200 lbs. It realises, 

 therefore, all the conditions required. It is coiled upon 

 a drum, and consequently does not prove an encumbrance ; 

 it is not heavy, and still it is capable of resisting the 

 severe strain required in drawing back the dredges 

 from great depths. The vessel carries also sounding- 

 leads of a new model for bringing to the surface the mud 

 from the sea bottom for the study of the numberless 

 organisms which swarm therein. Self-registering appara- 

 tus will record at every moment the condition of the 

 sea, the height of the waves, and the movements of the 

 vessel. Lastly, the improved dredges will enable the 

 explorers to search the abyss with more care than has 

 ever been done before. 



Amongst the instruments of an entirely novel type 

 embarked on board the Hirondelle, and doubtless des- 

 tined to yield unforeseen results, are what may be called 

 abyssmal traps. 



The article on the " Sea Dredge," Scientific News, vol. 

 ii., p. 60, has made everyone acquainted with the general 

 manner in which deep-sea dredging is effected. A kind of 

 large bag, held open by an iron frame, is attached to the 

 ship by a strong cable ; this drags the dredge after it, and 

 thus scrapes the bottom of the sea. It will be seen that 

 if this method be in a manner convenient, it is imperfect. 

 The dredge accumulates as much mud as animals ; how- 

 ever strong it may be it is liable to be torn upon the 

 points of rocks ; if it collects delicate organisms, which 

 often happens, it makes a complete paste of them. 

 Further, it catches only those animals which crawl at 

 the bottom. Every agile creature easily gets out of the 

 way. Hence we know little as yet of the wonders of 

 the abyss. Two of the explorers of the Hirondelle have 

 sought to entice the animals of the deep by means of 

 baited snares, and from this idea there have sprung 

 the baskets of the Hirondelle and the electric appliance 

 of Dr. P. Regnard. 



The traps are very like those used on our coasts for 

 catching lobsters, only in place of being a few inches in 

 length they are two yards. Our figure, taken from La 



