SEPTEMBER 14, 1916] 
NATURE 
29 
The binding screw (A) being free (or loose), the 
driving disc (B) is disengaged from the polar axis. 
On turning the winding-up wheel (C) the plunger (D) 
is drawn out of its cylinder (E), sucking oil into the 
cylinder from the reservoir (F) through a valve. The 
winding-up has also turned the driving disc (B) and 
lifted the driving weight (G). When the winding-up 
is finished, the cylinder (E) is full of oil, which is 
imprisoned by the automatic closing of the valve from 
the reservoir (F). The oil is now under pressure, 
caused by the driving weight (G), and it can only get 
out of the cylinder (E) back to the reservoir, through 
a hole, the size of which is controlled by the regu- 
lating screw (H). If the binding screw (A) is now 
screwed fast, the telescope will turn on its polar axis 
at the rate allowed by the regulating screw (H). 
An oil possessing a high flash point is suitable for 
this purpose, since the change in viscosity under 
different temperatures is then not much felt. A 
change in the viscosity causes the oil to pass through 
the valve at a correspondingly different rate. Hence 
it is necessary to adjust the valve to the local tempera- 
ture, which is done by setting the regulating screw 
according to the positions representing degrees of tem- 
perature, which are marked round the top of the oil 
reservoir. The regulator runs for three hours before 
re-winding, the oil, of course, being used over and 
over again, 
In a mechanism of this nature it is evident that the 
question of friction is of the first importance, and great 
care has been taken, first, to reduce the working 
friction to a minimum, and, secondly, to make the un- 
avoidable friction as constant as possible. The polar 
axis is therefore fitted with three sets of ball bearings 
(two axial and one thrust); the guide pulleys are also 
fitted with ball bearings, and the plunger is ground 
truly parallel and very smooth. 
The regulator is intended more especially for eclipse 
and visual work in general. -There are slight errors of 
NO. 2446, VOL. 98] 
| a note within a few semitones of the wolf-note. 
motion which have yet to be overcome, and they 
render it difficult to keep a star on the wire; but by 
an additional contrivance which has yet to be adapted 
the errors in question might be reduced sufficiently to 
render the device suitable for stellar photography, 
' ScCRIVEN Bo.ton. 
The Observatory, Bramley, Yorkshire, 
August 23. 
On the ‘‘ Wolf-note’’ of the Violin and ’Cello. 
In a letter to NaTurE (June 29) on the wolf-note of 
the violin and ’cello which has recently come to our 
notice, Mr. Raman referred to a paper by one of us 
(G. W. W.) on the subject. We had anticipated being 
associated in a joint paper dealing more fully with the 
results when the war put an end to the work. 
At the time when the preliminary results were pub- 
lished the cyclical variation in intensity of the wolf-note 
was provisionally attributed to the beating of the 
oscillations of the two tuned resonators, belly and 
string, “coupled” together by the bridge, and not to 
transitory beats, as perhaps justly inferred by Mr. 
| Raman from the wording of the paper, it being 
assumed that the strong reaction of the belly on the 
string interfered with even bowing. But the later 
results we obtained could not be reconciled with such 
a view, and we were seeking an explanation on the 
| lines of that now given by Mr. Raman. 
Thus further records of the wolf-note showed very 
clearly indeed the prominence of the octave at the 
minima in the belly records. Also simultaneous records 
of belly and string vibrations led, in the case of one 
‘cello, to curves practically identical with those given 
by Mr. Raman, in which the maxima and minima of 
belly amplitude lag behind those of the string by a 
quarter of a cycle. With another ‘cello of brilliant 
quality no appreciable lag appeared to exist, though 
perhaps better photographs would have shown some. 
Finally, the frequency in variation of intensity seemed 
| to depend on the speed of the bow and not on the 
form of the bridge, which would affect the degree of 
coupling. 
We take this opportunity of recording two other 
results obtained by us, which furnish still more 
evidence for the belief that the wolf-note is a pheno- 
menon accompanying maximum resonance. They are 
worthy of record, because this interpretation of the 
effect is not that which is held generally by musicians 
and instrument-makers. 
The first was obtained in some experiments on “ the 
mute.”” With the two ’cellos with which observations 
were made, the effect of loading the bridge with the 
mute was a reduction in pitch of the wolf, by 
an amount depending on the form of the mute. 
Thus, with one heavy mute the pitch was lowered from 
G to D, and with a lighter mute from G to E. By 
blowing a cornet in front of the belly, it was found 
that the natural frequency of the belly was correspond- 
ingly lowered. 
The second was obtained when vibrations of the belly 
were set up by plucking a string. The transitory beats 
present in the early stages of a forced oscillation were 
very clearly shown. The G string was plucked to give 
After 
six.or seven beats the belly took up the sinusoidal vibra- 
| tion of the string, which persisted until the sound was 
| that given by the cornet. 
no longer audible. Calculations of the natural period 
of the belly from the frequency of the beats led in each 
case to a period the same as that of the wolf-note and 
A. M. TynDALt. 
G. W. Wuite. 
University of Bristol, September 1. 
