Nalural-Philosophical Colleciiont, 67 



descence ; and, in support of his opinion, he has caused to be prepared a mean 

 teble of the price of com in England, and of the number of spots which have been 

 seen each year. He thinks that he has thus found a proof of the accuracy of his 

 views ; for the years when the spots were most numerous, the crops were mo* 

 abundant. 



Every one is aware of the uncertainty which such evidence must involve ; but 

 the opinion of Herschell is nevertheless very plausible, and the question is one of 

 the most important which can occupy the attention of astronomers. M. Arago 

 has taken tlie true means to solve the difficulty, by noting every year the num- 

 ber and dimensions of the sun's spots. There can be no doubt that these obser- 

 vations, wlien they have been repeated during a certain number of years, will 

 serve to decide with certainty whether there be any relation between the spots of 

 the sun and the heat of the seasons. We trust that all astronomers will conair 

 with him in a labour, on whose importance, whatever may be the result to which 

 it will lead, there cannot be two opinions — Le Globe. 



Extract from the Analysis of the Labours of the Academy of Sciences, dur- 

 ing the year 182B ; by Baron Fourier. (Concluded.) — M. Girard, on the 

 31st March, read to the Academy a Memoir, which is to be printed in the ninth 

 volume of the collection, and of which the following is the title : — Memoir on 

 the laying of water-pipes in the city of Paris ; tables and descriptions of ex- 

 periments made with reference to this subject on the expansion of cast-iron. 



This memoir bears upon a very important public use. The author, who to 

 the most extensive experience adds the light of scientific knowledge, has deduced 

 from observations made with great care, and from the application of the mathe- 

 matical sciences, several remarkable consequences which we shall briefly indicate. 



A pipe composed of leaden or cast-iron tubes, connected together in a series, 

 may be considered as a single metallic rod, capable of being condensed or ex- 

 panded by tlie diminution or augmentation of the temperature. The variations 

 which this rod undergoes in its length are so much the more sensible the greater 

 this length itself is ; and the ruptures to which water-pipes are generally subject 

 in the changes of the seasons, are almost always owing to these variations of 

 length. 



Agreeably to the arrangement pointed out by the author, and which has been 

 adopted, the pipes intended for the distribution of the waters of the Ourcq, in the 

 city of Paris, have been placed in arched galleries. It was therefore possible to 

 remark each day, and each hour, the influence of temperature upon the diminu- 

 tion and increase of length. M. Girard selected for this purpose four pipes, each 

 680 metres in length, and placed in the same gallery, parallel to each other. 

 Each of these pipes was divided into five parts, the extremities of which could 

 slip into each other, so as to allow the length to which they were thus encased, to 

 be measured. 



In order to render more easy the motion by which this was to be effected, one 

 of the four pipes was placed transversely on cast-iron rollers. The others were 

 merely placed on pieces of oakwood. Things being thus arranged, the obser- 

 vations were commenced on the 13th January 1812, and were terminated on 

 the 17th December 1815. During this period, the number of these observations 

 amounted to upwards of 650. The temperature of the water varied in these pipes 

 from 0° to 174 degrees of Reaumur's thermometer, and it was found that the 

 linear expansion of the cast-iron varied equally for each degree, and that it was 

 for the length of G80 metres, 0m.00C810 in the pipe which was placed upon the 

 rollers, while it was only 0m,0059G5 and Om.OOCSlB in the other two which 

 were placed upon pieces of wood. 



The author had occasion to remark, that the true temperature of the pipes ex- 

 perimented upon was neither that of the water with which they were tilled, nor 

 that of the air of the gallery in which they were placed, but a temperature inter- 

 mediate between that of the internal water and that of the external *ir, which 

 were always different. " - • .. •■ 



