HARDWICKE'S SCIENCE-GOSSIF. 



255 



Passing on, I picked up seaweed of several kinds, 

 nearly every specimen of which was encrusted with 

 a coralline substance, bristling all over with long 

 hairs. Hundreds of such specimens could have been 

 collected in a few minutes, on large Ftcci and 

 Laminaria, as well as delicate Rhodosperms. Here 

 was another example of homes without hands, for 

 even the pocket lens showed the openings to hun- 

 dreds of cells, armed at the mouth with long spines ; 

 and this commonest of zoophytes (as it is often 

 called) was the Membranipora pilosa (fig. 152). 



Fig. 153. Membranipora pilosa, x 60. 



Here then are four very interesting and very 

 common objects, each having its own story, and a 

 marvellous one too, of low life beneath the ocean- 

 wave. All these were picked up within a few yards 

 and during an interval of not more than five minutes ; 

 yet, if their stories were fully unfolded, these would 

 occupy as many hours. I wonder how many of the 

 thousands that rush to Hastings, and such-like 

 places in the autumn, and kick these objects along 

 on the sand, ever think of the story that they could 

 reveal, or dream of questioning them concerning the 

 living wonders of the sea. 



VALLEYS AND HILLS. 



QINCE living at the embouchure of the lovely 

 ^ St. Austell valley, I have been often asked, 

 why valleys during the night should be so much 

 colder than hills around them ; aud as many edu- 

 cated persons to whom I have proposed the 

 question have been at a loss for an explanation, 

 perhaps the few following remarks on the subject 

 may prove interesting to some of the readers of 

 Science-Gossip. Heat, as is well known, has a 

 tendency to expand all substances into which it 

 enters, and thus the specific gravity of bodies will 

 be lessened by it, so that heated air will be lighter 

 than air of a lower temperature, and cold air will 

 sink by its greater weight to the lowest place. Let 

 us suppose that various atmospheric currents, of 

 different degrees of heat, are commingling and roll- 



ing over the higher parts of a neighbourhood ; it is 

 clear that the valley, as the lowest place, will most 

 probably get more than its proper share of cold 

 vapours, by the simple laws of gravitation ; and hence 

 one reason why valleys at nights are often much 

 colder than hills. Again, it is a fact, that to convert 

 water into invisible vapour, six times 180° of heat 

 are necessary, or six times the amount of caloric 

 required to raise water from the freezing to the 

 boiling-point ; and as every cloud consists of this 

 wonderful expansion of water, and watery particles, 

 and store of latent heat, it is easy to understand, 

 if clouds are more frequently condensed into 

 rain on the hills than in the valleys, that the tem- 

 perature of the more lofty districts of a neighbour- 

 hood must, in this way, be raised. Now, observa- 

 tion has proved that such is the case, and reflection 

 shows why it should be so ; for if the pressure of 

 the atmosphere in the valley be 15 lb. on the square 

 inch, when the barometer is at 30°, the barometer 

 1,000 feet up the hill-side would stand only at 29°, 

 proving that ^th part of the whole atmosphere 

 existed in the stratum beneath, and if so, that the 

 pressure at that height would be only 14i lb. to the 

 square inch ; the air, therefore, 1,000 feet up, being 

 less dense, would have 5 'oth less sustaining power of 

 the clouds drifting through it ; and if to this rarity 

 from loss of superincumbent weight we add the 

 steady decrease of temperature from dilutation of 

 the air and loss of reflected heat from the earth 

 itself, it is not difficult to understand why condensa- 

 tion shouldjtake place on the hill-sides. Of course, 

 this explanation will apply only to moderate heights, 

 to lines below perpetual snow, for the precise point 

 must exist on every mountain, varying with its lati- 

 tude, where the amount of caloric given out from 

 condensed vapour will be more than counterbalanced 

 by the cold caused by increasing dilutation of the 

 atmosphere. Again, if it be true that valleys are 

 colder than hills by night, they are much warmer by 

 day, from concentration of the sun's rays and absence 

 of fierce winds. And often, even in the night, when 

 the thermometer notes many more degrees of heat 

 on the hill-side, the temperature in the valley may 

 be more endurable than the rapid evaporation caused 

 by a dry wind ; for it must not be forgotten, that 

 whether steam be formed by the bubbling of boiling, 

 or silently passes away by evaporation, the amount 

 of caloric it carries with it is always the same, and 

 the heat which makes it must be abstracted from 

 something. Goethe makes the following sensible 

 remarks in one of his letters from Italy :— " Auf dem 

 flachen Lande empfangt man gutes und boses 

 Wetter, wenn es schon fertig geworden, im Gebirge 

 ist man gegenwartig wenn es entsteht ; denn nicht 

 die Polhohe allein macht Klima und Witterung, 

 sondern die Bergreihen, besonders jene, die von 

 Morgen nach Abend die Lander durchschneiden." 



Joseph Drew. 



