584 Chronicles of Science. [ Oct., 
In a letter addressed to Professor Leonhard,* Dr. Sandberger 
notes the discovery of Tridymite in the cavities of a trachyte from 
Mont Dore les Bains, where it is accompanied by rock crystal. 
The two dimorphic forms of crystallized silica are thus presented 
in association. 
Everyone must have experienced the difficulty of retaining in 
mind for any length of time the formule of minerals which pre- 
sent a complex constitution, notably those of the compound silicates. 
To assist in overcoming this difficulty the Rev. B. W. Gibsone 
suggests the employment of a mnemonic system.t Using consonants 
to represent the digits, he forms memorial words associated in a 
fanciful manner with the minerals to which they relate, and then 
throws the whole into rhyme in order to fix it the better in me- 
mory. Some of these rhymes form such frightful jargon that we 
could not disgrace our pages by transcribing them; but to give 
our readers a notion of this kind of memoria technica we may pick 
out one or two of the best couplets. Here is one: 
“ Heat Topaz and its tint will fade ; 
Of murder Scapolite’s afraid.” 
Here is another : 
“* Never smoke Meerschaum, or the croup 
Will hurt Picrosmine’s heart.” 
In these examples the memorial words are italicized. Thus, 
in the first line, the word fade, when translated into figures, gives 
for Topaz the value of the numerical constants in a standard 
formula. With the exception of students who are cramming to 
satisfy over-reaching examiners, there are probably few who would 
be willing to rely upon a system so essentially artificial. 
For the third time during the present century the province of 
Casale, in Piedmont, has been the scene of a shower of meteoric 
stones. On the 29th of last February, at about 10 a.m., explo- 
sions were heard over a considerable area, and small clouds were 
observed at a moderate height rapidly moving from N.W. to 8.E. 
These phenomena were followed by a fall of stones, witnessed by 
several labourers, and at one place a peasant’s hat was actually 
struck by a meteoric fragment. Although several stones were seen 
to fall, only a few pieces were afterwards found. As usual, the 
stones were coated with a hard black varnish-like crust, and on 
fracture they presented a lighter colour and a fine texture some- 
what resembling that of trachyte. ‘The fall occurred between the 
villages of Villeneuve and Motta de’ Conti. The stones from the 
latter place were too small for quantitative examination, but those 
* Neues Jahrbuch f. Mineralogie, us.w. 1868, Heft IV., p. 406. 
+ Aide-mémoire for siliceous formule. ‘Chem. News,’ Aug. 21, 1868. 
