294 4 
Ji\ rs WI OM Sg am 
[ JANUARY 28, 1897 
The “* poundal” system is equally objectionable theoretically 
/ 
( witness Prof. Lodge’s formula s = >) and is not in practical 
z 
use. 
Then why introduce it? C. S, JACKSON. 
Conductorless X-Ray Bulbs and Tubes, 
In October 1896 (NATURE, vol. liv. p. 594), a description 
was given by me of an exhausted bulb used in conjunction with 
a Tesla coil which gave X-rays and its photographic effects. 
Since these experiments I have found other phenomena, 
which throw some light on the relative positions of the con- 
ductor carrying the oscillations and the greenish fluorescence 
within the bulb or tube. The relationship is shown in the 
following diagrams :— 
(1) A B is the conductor, with its axis parallel with ox, 
carrying the oscillating current of the Tesla secondary coil ; 
SS the exhausted sphere, F D Ea ring of greenish fluorescence, 
the plane of the ring being at right angles to the axis of the 
conductor AB. The X-ray effects were strongest at D, a point 
in OY furthest from the conductor AB. The limits of the position 
of the edges of the fluorescence were easily traced by means of 
a minute fluorescent screen, placed at the end of a vulcanite 
tube, furnished with a cup-shaped end to cover the eye. 
Fic. 1. 
When the sphere was rolled, or moved parallel with itself 
along the length of the conductor, the plane of the glow-ring, 
DE, kept its original position and moved perpendicular to the 
conductor. I have not been able to obtain the effects from an 
oretnaty induction coil giving an 8 cm. spark only with the Tesla 
coil. 
An exhausted tube was next placed within an open coil carry- 
ing the Tesla oscillations ; the following beautiful effects were 
produced. 
AB, exhausted tube ; CCC, the spiral conductor; DDD, the 
glow in the form of a spiral within the tube. When the glass 
tube was about 4 mm. internal diameter, and the conductor, a 
gutta-percha covered copper wire, touched the glass, the spiral 
glow was very bright, and the glass became warm. 
Fic. 2. 
If a cross section be made through the tube and wire at right 
angles to the axis of the tube, a point in the glow is situated 
180° from a point in the conductor, the section of the axis, the 
central point, being taken as the origin. The Tesla spark in air 
was 5 mm. long, and the coil formed a part of the spark circuit. 
Oxford, January 14. FREDERICK J. SMITH. 
Patterns produced by Charged Conductors on 
Sensitive Plates. 
IN reply to the request of Mr. J. I’Anson for a reference to 
any former observations on the interesting effects described in 
your current number, he will find in the B.A. Report for 1888, 
and more fully in the Phzlosophical Magazine for December of 
that year, an account of the phenomenon as observed by the 
present writer, using cut-out patterns of tinfoil as conductors. 
This action of electrified conductors in contact with the photo- 
NO. 1422, VOL. 55] 
grap}yic film was subsequently employed in a refined way by 
Rey. 1°. J. Smith, in making very beautiful and interesting prints 
from electrotype and other printing blocks. His results were 
shown at a conversazione of the Royal Society on May 10, 
1893. 
My own paper was chiefly occupied with a description of the 
figures produced by allowing sparks from an induction coil to 
play in various ways over photographic plates; and now that 
induction coils have become so much more widely distributed, 
it seems worth while to again draw attention to the exceedingly 
beautiful and interesting effects easily produced in this way. 
A very fine set of prints from similar spark traces was exhibited 
by Mr. A. A. C. Swinton, at the Royal Society’s conversazione 
cal 1892. J. Brown. 
Belfast, January 22. 
The Problem of the Sense Qualities. 
(1) In his very friendly notice of my ‘‘ Outline of Psychology * 
(NaruRE, December 10, 1896), Mr. W. E. Johnson points out 
what he takes to be a fallacy underlying the calculation of the 
number of possible sensation qualities in that and other text- 
books. I believe with Mr. Johnson that the qualitative series is 
in many cases (not all: cf taste, e.g.) continuous. But I do 
not think that this makes the calculation of distinguishable 
qualities fallacious. 
Mr. Johnson's argument is briefly as follows :—Let A BC D 
be stimuli of the same physical continuum (e.g., wave-lehgths), 
whose values are such that the sense qualities corresponding to 
A and D are just noticeably different. Then we have :— 
Stimulus Bec ee sae A B Cc D 
Sensation ag ao wae a [4] [e] ad; 
and the syllogism runs :— 
a is not d, 
bis a, 
“.@ is not d. 
But by hypothesis, @ is 4, being indistinguishable from it. 
Hence to make difference = distinguishableness in calculation 
leads to a logical fallacy. 
If now it were a case of diversity in logical predicate zs. 
identity in experience, the psychologist would be found to decide 
in favour of experience. But I think that the whole syllogism 
is erroneous. Asa matter of fact, going from left to right, we 
have the series :— 
Stimulus ae ae a0 A B (C D 
Sensation ua a ond a a a ad 
and, going from right to left, the series : 
Stimulus A ras aS A B (E) D 
Sensation ber a ae a a th d 
from which the only conclusions are :— 
Some a is not d, 
Someaisd,... 
z.é., two particular propositions. It is of the very essence of 
the just noticeable difference that it is cognised under certam 
conditions, and not under all. 
So far, then, the fallacy turns out to be imaginary. There 
are no sensations 4 and c, qualitatively distinct from a@ ord. Nor 
can there be, whatever value of stimulus be taken as starting- 
point for the determination. An observer working with stimuli 
BCODE.... would get the sensation series d6e7m... 
which would be qualitatively indistinguishable from the series 
EAU oe a 
Calculation of qualities by arithmetical progression  pre- 
supposes, of course, a constancy (found as in tones, or calculated 
as in colours) of the adsolute difference limen. Weber's law 
holds only of sensation intensities, which I expressly decline to 
calculate (p. 70). There is one qualitative series in which a 
uniformity resembling Weber’s law obtains: the black-white 
series. But this series isin many respects anomalous, its qualities 
seeming to have the function of visual intensity ; and neither 
its physiology nor its psychology is at present very satisfactory. 
(For the calculation of the number of brightness qualities, see 
Prof. K6nig’s paper, Ebbinghaus’ Zed/schrift, vol. viii. pp. 
377 ff.) 
(2) Mr. Johnson further objects to my analysis of the process 
