74 



SCIENTIFIC NEWS. 



[July 27, i£ 



about 65 degs. measured from the centre, it became lost 

 to sight, reappearing on arriving at an angle of about 

 55 degs. to 60 degs. as a dark spot, which in a short 

 time occupied in further progress became as black as its 

 shadow. The effect was not a little surprising, seeing 

 that it was totally unexpected." 



Mr. Spitta's expression of angles in the above require 

 explanation, his zero being the centre of the circular 

 image of the sphere as seen in the telescope, and his 90 7 

 being the circumference or limb ; the intermediate angles 

 of course in accordance with this. 



It was evident from the results of the previous experi- 

 ments thaL these changes were due to-differences of albedo 

 in different parts of the sphere, as the flat disc of the 

 moons could not thus vary, and, therefore, a positive 

 determination of such variations became a work of con- 

 siderable interest. 



Mr. Spitta accordingly proceeded with this investiga- 

 tion, using the wedge photometer, which is a long wedge 

 of glass originally used by its inventor, Prof. Pritchard, 

 of Oxford (" the heavenly body," as the naughty boys 

 there call him), for determining the so-called " magnitude" 

 of slars by first inserting the thin end of the wedge 

 between the observer and the star, proceeding until the 

 light of the star is extinguished, and then noting the 

 thickness of glass which produces this effect. This in- 

 strument was applied by Mr. Spitta (with precautions 

 and modifications that space will not permit me to 

 describe), to determine the albedo of his mcdel planet, 

 which he found to vary as follows. 



Over a circle extending from centrality or o° of Mr. 

 Spitla's measure to .30° in all directions the albedo was 

 not perceptibly altered. It was that of the material, and 



is represented by the figure. 

 At 40 it was reduced to 



» 5° 17 t> 



» 6o » ,, 



j> °5 >■> >} 



„ 7° „ » 



;j 75 )> >> 



;> 8o ;; » 



» °3 >> j; 



„ 86-30' „ „ 



0'735 

 0-500 

 0-367 

 0-323 

 0-261 

 0-17-2 



0-133 



o - o8o 



0-049 

 0-027 



The decrease with obliquity is thus seen to accelerate 

 rapidly, the loss approaching approximately to the 

 tangent of the angle. 



Here we have a curious physical fact, a strange optical 

 illusion. If we look at a sphere such as a planet reflect- 

 ing the sun's light, or a plaster-of-Paris ball reflecting a 

 strong artificial light and placed at a considerable dis- 

 tance, we see a small disc which appears to be about 

 equally luminous all over, but it is not so, nor nearly so. 

 We are violently deceived either by irradiation or 

 some other optical proceeding not at present under- 

 stood. 



Adaptation of Structure to Habits. — Says Mr. F. 

 P. Pascoe, F.L.S., in an interesting work on " Natural 

 Selection": "We admire the structure of the fore- 

 limbs (so well adapted for burrowing) of the mole ; but 

 the rabbit, an unsurpassed burrower, is no more adapted 

 for burrowing than its congener the hare, which never 

 burrows. The common snake (Tropidonotus natrix), 

 without fins like the viper, is a rapid and graceful 

 swimmer, while the latter rarely goes near the 

 water. ' 



THE NATURALIST AT THE SEA-SIDE. 

 III. — Shore Collecting. 



THE most discouraging circumstance about sitting '■» 

 down to write a short article on shore-collecting is' i 

 that the thing has been done very well already. Lewes, 

 Gosse, and Kingsley have all put on paper their own 

 experiences, and being practised writers as well as keen 

 observers, they were able to write lively and profitable 

 sketches. However, their books are not in every house, 

 and some of our readers, looking forward to seaside 

 rambles, may be glad to be told how to set about shore- 

 collecting. 



Our first remark will be disappointing to some. 

 There are many seaside, places of popular resort likely 

 to be fixed upon for a summer holiday where little can 

 be done in the way of collecting plants or animals. A 

 sandy shore is unpromising ; so is the neigbourhood of 

 a big, muddy river. It is true that even in such places 

 as these the trained eye will find something of interest, 

 but to the beginner they are barren. The good collect- 

 ing grounds are rocky coasts, with deep, clear water, and 

 shady pools overhung by boulders. As to time, the 

 spring-tides (new and full moon) are much the best. 

 For tackle, a shallow basket of no great size, jars of 

 various kinds, and a hand net of strong muslin will be 

 found indispensable. A small crow-bar and a stout 

 hammer are desirable. It is hard to carry about all the 

 implements which are likely to be wanted, and for this 

 and other reasons a small party will usually fare better 

 than the solitary rambler. Let us visit in the first place 

 a rock-pool at low water. Hydroid zoophytes, polyzoa, 

 anemones, ascidian colonies, and small fishes may 

 be met with in such haunts. Lively little crustaceans 

 will give employment to the net. Medusoids, left by 

 the tide, may be seen pulsating in the clear waters. 

 Another productive ground is to be met with around big 

 blocks of stone. Turn over such as are not often shifted 

 by the waves, and you will often find curious marine 

 worms, some of monstrous size. To make the most of 

 a good bit of shore the collector must not be afraid of 

 wading out at low tide. He should leave his stockings 

 at home, and walk out in strong shoes only. 



We advise those who mean serious work to bring 

 back as much live stock as possible. Things that have 

 dried in the sun, or have been shaken up with stones 

 and sand, are seldom fit for real study. But many 

 treasures of the deep, brought home in salt water, will 

 live long in an extemporised aquarium, and may be 

 anatomised or microscopised at leisure. Let the reader 

 avoid the common delusion that to glue dried organisms 

 upon white cards is useful work in natural history. A 

 certain amount of thought must be put into every 

 occupation if it is to turn out really productive. You 

 cannot go far wrong if you set yourself steadily to make 

 out points of structure, or to observe the mode of life of 

 anything that crawls or swims. Have a note-book always 

 at hand, and make endless drawings. 



A very serious difficulty which besets the beginner is 

 to make out what he has got hold of. Even the prac- 

 tised zoologist often needs a whole library of books to 

 name his specimens. But if the determination of species 

 be left to experts, a mere novice may hope with a little 

 time and patience to find out what kind of animal he has 

 before him. A living teacher is best by far, and a 

 course of practical zoology gone through in advance will 

 save much labour. So will a few visits to any tolerable 



