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  6 C U R R E N T T O P I C S . [ J. F . [.

the forces concerned cause the gas to remain attached during a fall

through a distance of 5° cm. Moreover adsorption is selective as is

demons tra ted by the change in the composition of the gas. The

experiment speaks against Harkins' method of measuring surface-

tension. G.F.S.

T h e F o u n d a t i o n o f E l e c tr o m a g n e t i sm ( I s i s , June, I 9 2 8 . To

Hans Christian Oersted we owe the discovery of the magnetic

effects of the electric cur rent. He was born on a Danish island in

I777, became professor in the Universi ty of Copenhagen and died in

I85I. The experiments which he began in April I82o are amongthe most memorable in the whole history of science. Th ey enabled

him to correlate two departments of natural philosophy, hitherto

separate, electricity and ma gne ti sm- -an d thus to carry one step

further the unification of knowledge.

There is given a facsimile of a lithographic portrait of Oersted

made by his compatriot Bearentzen who in making his likenesses

used to draw directly on the stone. Two papers of Oersted are

presented in facsimile, one his account in Latin of his discoveries

and the other the English translation of the same paper, sent to theAnnals of Philosophy. Both bear the date of July 2i, I82o, and

both describe the author as Kn ig ht of the Order of Danneborg,

Professor of Natural Philosophy, and Secretary to the Royal

Society of Copenhagen. The title in English is Exp eri ments on

the Effect of a Current of Electricity on the Magnetic Needle.

This, however, is a free translation of the Latin heading Experi -

menta circa Effectum Conflictus Electrici in Acum Magneticam.

What the Latin words for conflict of electri city meant is explained

in the English text where in regard to a wire connected to the endsof a galvanic ba tt ery it is said T o the effect which takes place in

this conductor and in the surrounding space, we shall give the name

of the c o n f l i c t o f e l e c t r i c i t y . The 'electric conflict' then includes

both the electric curr ent and its magnetic field. For example it issaid I t is sufficiently evident from the preceding facts that theelectric conflict is not confined to the conductor, but dispersed

pret ty widely in the circumjacent space. It is indeed surprising tonote how well Oersted gets along without any equivalent for the

modern expression 'the electric current .' He is definite by statingwhich end of the wire receives positive or negat ive electricity, though

references to negative electricity preponderate .It seems tha t others had previously sought in vain for an effect of

open galvanic circuits upon the magnetic needle. Oersted in thewinter of 182o found an effect to occur provided the circuit be

closed, or, as he qua int ly phrases it, the galvanic circle must be

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M ~ t I . , l U 2 9 , 1 CURRENT TOVlCs 7

c o m p l e t e . H e r e p e a t e d t h e e x p e r i m e n t s u s in g a s t ro n g e r b a t t e r y

a n d g i ve s t h e n a m e s o f s ix m e n w h o w e r e w i t ne s se s . T h i s m e t h o d o f

a t t e s t i n g t h e c r e d i b i l i ty o f d i s c o v e ri e s h a s i ts m e r i t s . H a d B l o n d l o t

a n d C h a r p e n t i e r f o l l o w e d t h e e x a m p l e of t h e D a n i s h i n v e s t i g a t o r

p e r h a p s t h e m y t h o f t h e N r a y s w o u l d n o t h a v e a r i se n a q u a r t e r o f a

c e n t u r y a g o .

T h e s c ie n ce o f e l e c t r ic a l m e a s u r e m e n t s w a s n o t y e t b o r n f o r w e

r e a d A s m a l le r a p p a r a t u s w il l a n s w e r p r o v i d e d i t b e s t r o n g e n o u g h

t o h e a t a m e t a l l i c w i r e r e d h o t . A s t r a i g h t pi e c e o f w i r e c o n v e y i n g

t h e e l e c t r ic c u r r e n t w a s t r i e d in v a r i o u s p o s i t i o n s i n r e l a t i o n t o t h e

n e e d l e a n d t h e d e f l e c t io n s n o t e d . T h e n e e d l e w a s s e e n t o b ed e f l e c t e d i n a h o r i z o n t a l p l a n e o r a v e r t i c a l p l a n e a c c o r d i n g t o t h e

l o c at io n o f t h e w i r e a n d v e r y a c u t e l y t h e c o n c lu s i o n is d r a w n t h a t

T h e e f f e c t c a n n o t b e a s c ri b e d t o a t t r a c t i o n a n d l a te r T h i s

c o n f l i c t p e r f o r m e s c ir c le s ; f o r w i t h o u t t h is c o n d i t i o n , i t s e e m s

i m p o s si b le t h a t t h e o n e p a r t o f t h e u n i t i n g w i re , w h e n p l a c e d b e l o w

t h e m a g n e t i c p o le , s h o u l d d r i v e i t t o w a r d t h e e a st , a n d w h e n p l a c e d

a b o v e i t t o w a r d t h e w e s t ; f o r i t is t h e n a t u r e o f a c ir c le t h a t t h e

m o t i o n s i n o p p o s i t e p a r t s s h o u l d h a v e a n o p p o s i t e d i r e c t i o n .

T h e n a t u r e o f t h e w i r e m a d e n o d if f e re n c e f o r W i r e s o f p l a t i n u m ,g o l d , s i lv e r , b r a s s , i r o n , r i b b o n s o f l e a d a n d t i n , a m a s s o f m e r c u r y

w e r e e m p l o y e d w i t h e q u a l s u c c e ss . M a n y d i f f e re n t s u b s t a n c e s

w e r e i n t e r p o s e d b e t w e e n t h e c u r r e n t a n d t h e n e e d le b u t a ll t r ie d

w e r e w i t h o u t e f fe c t. N o f e r r o m a g n e t i c m a t e r i a l w a s t e s te d . A

b r a s s n e e d l e a n d n e e d l e s o f g u m l a c a n d o f g la s s in t u r n r e p l a c e d t h e

m a g n e t i c n e e d l e b u t a l l r e m a i n e d u n d e f l e c t e d b y t h e c u r r e n t .

O e r s t e d c o n s id e r s b u t r e j e c ts a s v al u el e ss f o r e x p l a n a t o r y

p u r p o s e s a m o t i o n i n c ir cl es , j o i n e d w i t h a p r o g r e s s i v e m o t i o n ,

a c c o r d i n g t o t h e l e n g t h o f t h e c o n d u c t o r . T h i s , h o w e v e r iss u r p r is i n g l y r e m i n i s c e n t o f o n e m o d e r n m n e m o n i c d e v i c e f o r c o n -

n e c t i n g t h e d e f l e c t io n of t h e n e e d l e w i t h t h e d i r e c t i o n o f t h e c u r r e n t .

G . F . S .

A n A t t e m p t t o P o l a r i z e E l e c t r o n W a v e s b y R e f l e c t i o n . 7 . J .

DAVISSON AND L . H , GERMER. Na tu r e , N o v . 2 4, I 9 2 8 .) N o w

t h a t c e r t a i n s t r ik i n g r e s e m b l a n c e s b e t w e e n e l e c t r o n s a n d l i g h t w a v e s

h a v e b e e n s h o w n t o e x i s t i t i s q u i t e i n o r d e r t h a t s e a r c h s h o u l d b e

m a d e in t h e e n d e a v o r to fi nd a d d i t i o n a l si m i la r it ie s . T h e a u t h o r sw h o p r o v e d e l e c t r o n s t o b e r e f le c t ed f r o m c r y s t a l s m u c h a s l ig h t

w a v e s a r e r e f le c t ed f r o m m i r r o r s h a v e l o o k e d f o r e v i d e n c e t h a t u p o n

t h e r e f le c t io n o f e l e c t r o n s f r o m a c r y s t a l s o m e c h a n g e o c c u r s t h a t is

a n a l o g o u s t o t h e p o l a r i z a t i o n i m p o s e d u p o n l i g h t w h e n i t is r e f le c t e d

f r o m g la ss . T h e y r e p o r t S o f a r a s o u r o b s e r v a t i o n s g o, t h e r e is n o

p o l a r i z a t i o n o f e l e c t r o n w a v e s b y r e f le c t i o n . G . F . S .