Sept. 1st, 1887.] 



SCIENTIFIC NEV/S. 



151 



The Destruction of Stone.— In a recent number of La 

 Nature there was an article on the well-known causes of 

 the destruction of stone used for buildings. A correspon- 

 dent now points out that, in his opinion, there is another 

 cause which has not yet been spolcen of, and that it acts 

 upon the hardest and most resisting materials, such, for in- 

 stance, as granite. He refers to the sudden expansion pro- 

 duced by the sun while the temperature of the air is low 

 and the weather calm. Among the examples he cites is 

 the following : — At St. Pal-de-Mons {Haiilc Loire), in a 

 public place opposite the church, there is a cross which was 

 erected in 1670, as shown by an inscription on the stone. 

 The vertical limb of the cross is circular, and now presents 

 this peculiarity : a circular layer of the stone, about one 

 centimetre thick, has become detached from the inner por- 

 tion of the stone, and part of this outer skin or layer rests 

 against the inner trunk, but the other portion stands out 

 independently, and resembles the bark of a fossil tree. The 

 portion which rests against the trunk is on the south side, 

 and it is suggested that the phenomenon has been caused, 

 not by frost, but by a countless number of successive ex- 

 pansions and contractions produced by the sun. The climate 

 where this has occurred is cold and free from fog. The 

 occurrence is no doubt curious and interesting, but we fail 

 to see that there is any proof that it has been caused by the 

 direct action of the sun. 



Sanitary Action of Rain. — We commonly abuse our 

 climate on accounts of its humidity. This is a great mis- 

 take. Frequent and moderate rain, such as constitutes the 

 characteristic of tlie British climate, is the most efl'cctive of 

 all sanitary agencies. It cleanses the ground, and, what is 

 far more important, it cleanses the air. The ammoniacal 

 and other exhalations, continually arising from decompos- 

 ing animal and vegetable matter, are all more or less soluble 

 in water and are largely removed by gentle rain. Besiies 

 these it absorbs and carries down into rivers and thence to 

 the sea, the excess of carbonic acid exhaled from our lungs, 

 and produced by our fires and lights. De Saussure found 

 that a shower of rain removed about 25 per cent, of the 

 carbonic acid from the air over the Lake of Geneva. Also 

 that there was less over the lake than over the neighbour- 

 ing meadows and the great elevations of the Alps where 

 there was no water. The atmosphere over the sea con- 

 tains less than one-fourth of the quantity in that over the 

 land. Far away at sea the quantity is inappreciable, and 

 at a given place on the coast it varies with the wind, in- 

 creasing as it blows from the land, and vice versa. All these 

 facts show that water in contact with the air absorbs its 

 carbonic acid in a decidedly practical degree. In densely- 

 populated districts this is of considerable importance. The 

 difference is perceptible to the senses after a long drought, 

 as the common expression, " refreshing showers " indicates. 

 — Science Gossip. 



Height of Clouds. — Herren Ekholm and Hagstrom have 

 published an interesting summary of the results of observa- 

 tions made at Upsala during the summers of 1SS4-S5. 

 They determined the parallax of the clouds by angular 

 measurements made from two stations at the extremities 

 of a base of convenient length, and having telephonic con- 

 nection. They found that clouds are formed at all levels, 

 but that they occur most frequently at certain elevations or 

 stages. The following are, approximately, the mean heights, 

 in feet, of the principal forms : — Stratus, 2,000 ; nimbus, 5,000 ; 

 cumulus (base), 4,500, (summit) 6,000 ;cumulo- stratus (base), 

 4,600 ; " false cirrus " (a form which often accompanies the 

 cumulo-stratus), 12,800; cirro-cumulus, 21,000; cirrus, 

 29,000 (the highest being 41,000). The maximum of cloud- 

 frequency was found to be at levels of 2,300 and 5,500 feet. 

 Speaking generally all the forms of cloud have a tendency 



to rise during the course of the day ; the change, excepting 

 for the cumulus-form, amounting to nearly 6,500 feet. In 

 the morning, when the cirrus clouds are at their lowest level, 

 the frequencj' of their lowest forms — the cirro-cumulus — is 

 greatest ; and in the evening, when the height of the cirrus 

 is greatest, the frequency of its highest forms — the cirro- 

 stratus — is also greatest. With regard to the connection 

 between the character of the weather and the height of the 

 clouds, the heights of the bases of the cumulus are nearly 

 constant in all conditions. The summits, however, are 

 lowest in the vicinity of a barometric maximum ; they 

 increase in the region of a depression, and attain their greatest 

 height in thunderstorms, the thickness of the cumulo-stratus 

 stretching sometimes for several miles. The highest forms 

 of clouds appear to float at their lowest levels in the region 

 of a depression. 



Concrete Spoilt by Sea-Water. — A matter of the highest 

 possible importance and interest to all connected with the con- 

 struction and management of harbours has been brought to 

 light at Aberdeen. The Aberdeen Harbour Commissioners 

 opened a graving dock two years ago, formed of Portland 

 cement concrete, the steps being lined with granite ashlar. 

 A few months since it was noticed that the concrete entrance 

 walls, which are not lined with granite, had become swollen, 

 and that the surface had begun to show cracks. Investi- 

 gation as to the cause was at once made, and Mr. W. Smith, 

 the harbour engineer, suspecting that chemical action was 

 inducing the mischief, conferred with Professor Brazier, ot 

 Aberdeen University, who analysed briquettes of the Port- 

 land cement used in the construction of the graving dock, 

 and also samples of the concrete taken from the entrance 

 walls of the dock. From the analysis made it appeared 

 that the action of the sea-water on the Portland cement 

 itself, as well as on the cement in the concrete, caused an 

 expansion and softening of the cement in consequence 01 

 the deposit of magnesia from the sea-water, and also led to 

 the formation of carbonate of lime by the union of the car- 

 bonic acid contained in the sea-water with the lime in the 

 cement. This somewhat startling discovery must neces- 

 sarily receive great attention. Within the past quarter 01 

 a century a great number of sea-works have been formed 

 of Portland cement concrete. In the case of the graving 

 dock at Aberdeen it has required patching since its con- 

 struction fifteen years ago, but the idea that its defects were 

 due to chemical action did not occur to the harbour engi- 

 neer till last year. The remarkable point in regard to this 

 graving dock is the rapidity of the chemical action of the 

 sea-water upon it, as compared with the length of time that 

 similar action has had opportunity of taking effect on sea- 

 works. We understand the greater eflect is ascribed to the 

 fact that the pressure of the water in the dock is much 

 heavier than is the pressure of water on the sea -works. In 

 the former case the pressure is from five to eleven pounds 

 per square inch ; in the latter it must be very light except 

 when the waves drive heavily against the works. Till the 

 present time there does not appear to have been any inves- 

 tigation as to the chemical action of sea-water upon con- 

 crete. Now that science has been called in, and has made 

 the discovery that concrete must give way before the sea, 

 it will be the task of chemists to look out for some counter- 

 vailing substance which shall prevent the decay which 

 seems to be inevitable. It is something that science has 

 shown the danger that is being run ; it will redound more 

 to the honour of scientific men if they can indicate the 

 means by which the impending calamity can be avoided. 

 The subject came before the Harbour Board of Aberdeen 

 recently, and they resolved to hold a meeting of the whole 

 Board in committee to consider the matter. — Dundee 

 Aiivcrliscr. 



