CHARLES BABBAGE. 193 



whom they Lave, on any occasion, discovered traces of the artist. In 

 fact, the character of an observer, as of a woman, if doubted, is destroyed. 



The manner in which facts apparently lost are restored to light, even 

 after considerable intervals of time, is sometimes very unexpected, and 

 a few examples maj^ not be without their use. The thermometers 

 employed by the philosophers who composed the Accademia del Ciuiento 

 have been lost; and as they did not use the two fixed points of freezing 

 and boiling water, the results of a great mass of observations have 

 remained useless from our ignorance of the value of a degree on their 

 instruments. M. Libri, of Florence, proposed to regain this knowledge 

 by comparing their registers of the temperature of the human body and 

 of that of some warm springs in Tuscany which have preserved their 

 heat uniform during a century, as well as of other things similarly cir- 

 cumstanced. 



Another illustration was i)ointed out to me by M. Gazzeri, the pro- 

 fessor of chemistry at Florence. A few years ago an important suit in 

 one of the legal courts of Tuscany depended on ascertaining whether a 

 certain word had been erased by some chemical process from a deed then 

 before the court. The party who insisted that an erasure had been made 

 availed themselves of the knowledge of M. G dzzeri, who, concluding that 

 those who committed the fraud would be satisfied by the disappearance 

 of the coloring matter of the ink, suspected (either from some colorless 

 matter remaining in the letters, or perhaps from the agency of the sol- 

 vent having weakened the fabric of the paper itself beneath the supposed 

 letters) that the eft'ect of the slow application of heat would be to render 

 some difference of texture or of applied substance evident by some 

 variety in the shade of color which heat in such circumstances might be 

 expected to produce. Permission having been given to try the experi- 

 ment, on the application of heat the important word re-api3eared, to the 

 great satisfaction of the court. 



[One of the most noted deceptions of this kind was that called the moon 

 hoax, published in New York about thirty years ago, which purported to 

 be a series of discoveries made in the moon by Sir John Herschel during 

 his residence at the Cape of Good Hope. These discoveries were said to 

 be the result of a great improvement in the telescope. It is well known 

 that, with a given-sized object-glass, the power of this instrument is 

 limited by the degree to which the image in the focus of the glass can 

 be magnified; the light remaining the same, the more the size of the 

 image is increased the darker it becomes. The alleged improvement 

 consisted in the illumination of this image by artificial light. By the 

 application of this idea, the telescope employed by the astronomer at the 

 (jape of Good Hope admitted of an eye-glass of such magnifying power 

 that moving objects on the surface of the moon were observable, and 

 men and animals of remarkable forms were actually discovered. 



It is astonishing the effect which the annunciation of these discoveries 



produced. Instead of detecting at once the scientific absurdity of iliu- 

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