270 Mr. Tovey’s further Researches in the 
acid acted on chromate of lead and took up some lead, parti- 
cularly when the acid was for several days in contact with it: 
according to Mans, (Poggendorff’s Annalen, band ix. p. 127.) 
it is not soluble in acetic acid. 
Royal German Spa, Brighton, Gustavus SCHWEITZER. 
November 29, 1835. 
LV. Further Researches in the Undulatory Theory of Light. 
By Joun Tovey, Esq. 
To the Editors of the Philosophical Magazine and Journal. 
GENTLEMEN, 
oy that my paper on the relation between the 
length and velocity of a wave of light, inserted in your 
Number for January last, has received, in your Number for 
February, a favourable notice from your eminently scientific 
correspondent Professor Powell, I venture to send you a con- 
tinuation of my researches. 
My object now is to transform the general equations (3.) 
of that paper, into others adapted to any case of undulation 
in which the directions of the coordinates can be so taken 
that the displacements §, , , may be regarded as functions of 
z and ¢. 
On the condition just stated, we have, by Taylor’s formula, 
aye Me Ax Be Az® diz Axt 
Pi eet gas Bh) Gee hiae Vida ene 
ek) d*y Ax* O° 4 ee. ig ee 
BS ae date oo. Get hes cl aetna 
dé GO DOG? Ot a A ee cake 
Tek Tiga tt ag ga ges tng rel ara 
+ &e. 
+ &c. 
+ &c. 
Now, suppose the arrangement of the molecules in the state 
of equilibrium to be such that for every molecule on one side 
of m, within the sphere of its influence, there is another at 
an equal distance on the opposite side; then, if we substitute 
these expressions for A£, Ay, AZ, in the first of the equa- 
tions (3.), the sums =. ¢(7) Az, 2.¢(r) Aa’, TE. (r) A 2, 
Sais) Avy Z.v(nAyAx, z.v(r)AyAdc*, 
=. (r) AzAa’, E.(r) Az Azt, &c., in which the degrees 
of the products of the variations are odd, will vanish ; be- 
Cause, whatever be the signs of Aw, Ay, Az for any molecule, 
these signs will all be changed for the corresponding mole- 
