TO THE MOVEMENT OF MACHINES. 515 
too narrow ; at all events it ought to exceed half an inch. I have also 
made experiments with voltaic pairs arranged like the calorimotor 
of Hare, but there were reasons for rejecting these also. It is a very 
different thing to make an isolated observation, and to put in requisition 
the galvanic action for whole hours and days. It is in the latter case 
that for practical purposes measures are required, the necessity of which 
had not been before anticipated. It will be also necessary to reject the 
use of copper as a negative metal; the expense of employing silver, 
platina, or at least copper well plated with silver, gold, or platina, must 
be no obstacle. The solution of the copper in the sulphuric acid, how- 
ever weak it may be, and its reduction into a metallic state, by the se- 
condary effects of the nascent hydrogen, give rise to partial galvanic 
effects, by which the principal action is much affected, and to avoid 
which the greatest pains must be taken. In fact the motion of the 
magnetic apparatus was sometimes suddenly slackened or entirely in- 
terrupted, and on examining more closely I found that metallic parti- 
cles of cementing copper or of iron had been deposited all along the 
pieces of wood interposed, or upon the bottom of the troughs, and thus 
formed a partial circuit. I shall speak of zine hereafter. The following 
is the table of observations which I have made on the magnetic power 
-of the horseshoe bar of iron above dsecribed. 
No. 1./No. 2.} No. 3.|No. 4.|No. 5.|No. 6.|No. 7.| No. 8.]No. 9. 
.| Ibs. | Ibs. | Ibs. | Ibs. | Ibs. | Ibs. | Ibs. | Ibs. | Ibs. | Ibs. | Ibs. 
41°46 | 40°31] 47°19] 43°18] 45°47] 48°88] 46°52] 55°21] 55°21] 54°07] 47°75} 47°3 
126°32 |123°43 |125°21 |125°67 |128°47 |130°16 |124°39 | 120°55 |130°16 |130°16 |126°45 126 
156°98 |216°54 |180°04 |189°73 |184°34 }185°30 |205°91 }211 — |157°38 |162°77 |185 — |182°3 
201°72 |208°29 |195°14 |197-33 |199°99 |198°32 |201°25 | 202°92 |197°41 |203°83 |200°62 }216°1 
266°63 |243°21 |236°45 |235°65 |229°93 |232°75 |232°75 |228°79 |227°11 |227°11 |236°05 |236°3 
311°S {221746 |210°17 |198'88 |210°17 }198°88 |192°23 
144a* |258°56 |257°66 |254°46 |252°12 |256°22 |253-02 
The values given in the last column have been calculated according 
_ (233-6) x 
~ 9+a 
the method of the least squares. It is true that there are considerable 
differences between the observations of the same series, but there was 
no reason to choose those which agreed the best with each other, and 
to attribute the differences to an error of observation. 
to the formula A , the constants of which were found by 
10. 
I have read in an extract from the memoir of the Abbé dal Negro 
inserted in the “Annali delle Sc., 1813 [1833?], Marzo e Aprile, 
* The first series of experiments, which were made with the pair of plates of 
144 square inches, presented such different values that no use could be made 
of them. I have sought in vain for the cause of these anomalies. After a fort- 
night the experiments were repeated, and gave values but little different. This 
is proved by the Table. 
Vor. 1L—Parrt IV. Qn 
