32 Mr. C. HoltzapfFel on a Scale of Geometrical Equivalents 



phated oils with nitric acid, compounds are formed finally, 

 which resist the further action of the acid, and are only to be 

 decomposed by the assistance of a nitrate and deflagration. 

 I conjecture that these compounds will be found to merit 

 classification as aethers formed by an oxacid of nitrogen. 



One of my pupils, in examining one of the compounds 

 thus generated, was, as he conceived, seriously affected by it, 

 suffering next day as from an over dose of opium. He also 

 conceived that a cat, to which a small quantity was given, 

 was affected in like manner. 



I had prepared an apparatus with the view of analysing 

 accurately the various compounds above described or alluded 

 to, by burning them in oxygen gas ; when, by an enduring 

 illness of my assistant, and subsequently my own indisposi- 

 tion, I was prevented from executing my intentions. 



VIII. On a Scale of Geometrical Equivalents for Engineering 

 and other Purposes. By Mr. Charles Holtzapffex-, 

 Associate of the Institution of Civil Engineers. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 T^HE scale of geometrical equivalents is a particular com- 

 ■*- bination of several of the scales of equal parts, which 

 I have recently contrived and explained*: by means of this 

 instrument, with the aid of a little arithmetic, a great variety 

 of tedious calculations in constructive science generally, but 

 more especially in engineering, may be performed with con- 

 siderable correctness, by the simple inspection of scales, pro- 

 portionals to the quantities under observation. 



As regards drawing, the scales are shown to be only an 

 extension and generalization of the common application of 

 reduced scales of 1, 2, 3, &c. inches to the foot; and in their 

 application to numbers or quantity, they are laid side by side 

 with their zeros in contact, after the manner of thermometer 

 scales, two of which are frequently engraved on the same in- 

 strument for comparison, so that we may read the height of 

 the mercury either by the centigrade scale, freezing being 

 called zero, and boiling 100; or by the Fahrenheit scale in 

 common use in this country, the same space being divided 

 into 180 degrees, freezing being then marked 32. We may 

 thus transpose the French reading of the instrument into the 

 English, or the reverse. 



I have extended this latter application of scales to many 



♦ A new System of Scales of Equal Parts, by C Holtzapfi'el. 



