1922.] Indian Science Congress. 1.8.C. 171 
only way to do that is ee by direct frontal attack on atom struc- 
ture by bombarding matter with — had projectiles in the form of 
a particles from radium oa. and obse 
(a) what happens to the scales itp 
ig ye happens to the bombarded a 
may be — as the second Tin eo ot attack. I will first con 
see what has been done by Rutherford and — by the banibaat 
nt method the etn oink beginning about 
Phe ied fewmece of the experimental Soak is that each individual 
a particle bie se to a scintillation when it strikes a screen of zinc 
ene digi 
wa: slic m which had lost two electrons, probably external ones 
and therefore poss charge + 2e s it had only lost ois electrons 
it clearly possessed practically all the mass of the original helium atom 
and was regarded as sien the + portion of thea Its velocity from 
. to be about 2x 10% ems/gec, = iles/second 
If a steam of thes > high velocity, massive particles is fired at a thin 
plate of matter monet asa a film of gold, the ir behaviour on emerging from 
e film, can be exa a Zn sulphide screen held at a suitable 
distance. W Md have peal the particles even if they penetrated 
the film to be enormously scatter-d during the process. ne , 
least expect this pode if he voigatia the po 
bombarded atom to be of size comparable with the a parti It was 
however found by Geiger arsden that large majority e 
eP were very slightly deflected from their origi al direction, but 
that occasi lly an a particle suffer defile rare in- 
w it is not difficult to 
i negative errecire is negligible; so 
also would be the effect of a Tiabubid of + electricity over a sphere as 
eq 
an exceedingly small region, for if not the deflection a particles 
must have been both lar d numerous. If we call this inute massive 
portion the nucleu e atom, detailed calculation (based th 
i nownm S 
: nd 
charges of the a particle and bombarded nucleus) agreed extremely well 
with the deflections actuaily observed and also brought out two addi- 
epee oints :— 
The large deflections were ore to a single encounter and not to a 
number of small deflections superpos 
The colliding particles in ise case of the large deflections ap- 
2 one another hiboeie - distance of 10 
The good agreement of theory and experiment thus een very 
_. gaye that pres inverse square law the dis 
+6 ems. from the nucleus, and that the + — < the latter 
was Pdlatnbute over an ied minute aie n of s : 
spe most recent work of Rut therford is eve - eet “ ational me 
t was f f a pi es throug: 
as found that the fives ° : a p ic peyond the range as 
e rise to scintillations on a screen pla fi F 
Particles itself, four times as far in fact. The natural explanation the 
peared to be that the hydrogen atom or art of it ing shot forward by t 
collision. It was found, as the result of experim lied 
: atoms, whatev ey m . consist a were Se 
in che direction in which ¢ article ving. 
llh That ere velocities ek reap a a small range, ie. they 
all had nearly the same velocity. 
tance of 3x 10-15 cms 
3. That the. nuclii approached within a dis ssion for the num- 
during a collision. Now arwin has Semel an expre 
