166 Scientific Intelligence. — Natural History. 



they call them, which produce a visible silk, explains the procedure of 

 this little insect, whose work he compares to the spinning wheel of 

 the rope maker. Each spider is pierced with an infinite number of 

 holes, like the drawing plate of a gold wire drawer, and these holes 

 are so small and tight, that the space which a pin would occupy 

 would contain more than a thousand such. From each of these 

 issues a thread of inconceivable fineness, which instantly unites with 

 the others to form but one. The four spiders each making their 

 thread in the same manner and in the same time, the result is that 

 there are four threads alike, which, at the distance of about a tenth 

 of an inch, reunite also to form the silk that we are accustomed to 

 see, and which the spider makes use of to spin her web. Thus the 

 thread of a spider drawn by the smallest species, and so delicate that 

 the eye can scarcely perceive it, is not, as is generally thought, a sin- 

 gle thread, but in reality a cord which contains not less than four 

 thousand of them. 



But to understand perfectly this wonder of nature, it is necessary 

 to follow the calculations made by the learned Leuwenhoeck, agree- 

 ably to his microscopic observations. He has found that the thread 

 of the smallest spider, of which some are not as large as a grain of 

 sand, were of such a fineness that it would be necessary to unite 

 more than four millions to form the thickness of a hair. Now we 

 know that each one of this series is already composed of four thou- 

 sand threads ; it follows then that sixteen million of these threads, 

 drawn by the little spider, have not together the thickness of a hair. — 

 Jour, de Con. Usuel. VIII, 9. 



5. Phosphorescence of sea water. (Jahrbuch der Chemie.) — M. 

 PfafF, in a work on the coloring principle of the water of the Baltic 

 Sea, makes incidentally some remarks on the phosphorescence which 

 it presents, principally at the close of summer and in the autumn 

 until the month of November. He confirms, by a series of observa- 

 tions, the opinion that this phenomenon is owing to the presence of 

 microscopic animals, and chiefly of the infusoria. He remarks that 

 if an electric current be passed through a tube filled with sea water 

 recently drawn, there is immediately perceptible in it a multitude of 

 brilliant points, continually in motion, and which are visible only for a 

 few moments. In general, all the experiments prove that these mi- 

 croscopic animals produce the light which is peculiar to them, when 

 they are agitated in contact with stimulants, such as ammonia, acids, 



