the stead}' state has been established, In the discussion it
will bo assumed thai the motion of the ions 1% determined
wMl* by their positional and velocity eo^unhnule.s at emission
and by the electric field. The hnres e\eited by flu* inns on
ouch other1 and by moleeules <>t~ ;»;i:> into whose spheres of
notion they may ehamv t*» penetrate an* lett <»ut ni armunt,
These conditions art* reali/ed it'therunouie entrant ;*»i moderate
size are experimented with m hi;*h \arna, In filler tu avoid
complications arisinjj1 out <»i i'(*eotnbiu;ttion we shall also sup-
pose the teni}x*ralure t'owlilious to be ».ut h that ions nf OIK*
si^'n only oeenr, \Vc shall ni>w euu*«tdei the ;;ener,il pj'»tb!etu,
usin|»* redantjular et»«urdiiiafes,

Let thct eo-ordinatf*s ot'a p*»it»t <») the <.titt,j*e \ br* ij(r(, n
aiul let an ion lu^ projeeteil fi«»iu inr( M with tlf v* !m ity t nju-
pt>nents //ui?f,)*'i',f» I *et u?; seek the iutiditi«»n that lids shall
strike the surface II, who »e rqn.itinu is

$( i r- i «», , , » . f (^|i

within an infiniteMinal <Ii.»,tan«fe <»t flu% p»*iut i:i»'V '^ ^' *s
the potential at any point ufthe lie!*!, the e.|tutii»n, *•!' int»tiun
of the ion will be*

On integration tliese equations JMIT thiu-e fi jn din*!*, b»*tw<*(*ti

.r,j't ;:;» and / inv«>lvin;j *»ix arbitraiy lun'.i.iut . ults^haie deter,
mined by th<: valuta **t'Fj frf, .,rv, ,»',.,%, \ff^r elijninatnoi ul the*
time tlune rctutlt two etfti.ttlott'* wliiili may be wiit

'Jlie curvt? in which the ?ais face, *!», and <?« itji-r «.^* t i-, tfu*
lrajtt<;lory <»ftlui parti«'lt* projet ted uud»*r the j;isvn initial *'»»n-
<litions. I'he iutcnuiction of thi-t rurvr with ffp« ',uita<v

i|/-(,n/;j) - u j'jvts tht4 point when* the {nirli*. !e Jrik?*. tlu*
surface, The co-ordinate* .IJ»Y"I c^ <*!lr'1 P'uhtt'> uill theie*
fore b<Mn"ven by solving f jj), ;^s , uud ' i^,i for ,s» r, and %atif!

prohlnuf. t»i' flir ».uii»** ;;r«»«'ir*J iS-iiuttn in fhr
which tht* inlhu'Wtf of thr uuMtditu^ i<»u«-ih,nr Jirrit t»tkru IJIM
been eouwtlcml on ji, jy ;yul j». •;»»,ol. XVII, p. 813 (1909).n turn?* out to br oj thr -asn- i"in* a-. Ma\