Fuly 2, 1885] 
NATE RE 
197 
The latter has been growing much darker and more conspicu- 
ous during the last few months, and it seems very probable that 
this object may resume a good deal of its former prominence 
during the opposition of 1886. With my Io-inch reflector, 
power 252, I recorded the spot as passing the central meridian 
of Jupiter on June 26, 1885, at 7h. 59m., and to-night, June 28, 
at gh. 37m. A comparison of these times with the earliest I 
obtained during the present apparition (1884, September 21, 
18h. 28m.) shows that in the interim of 279d. 15h. gm. the spot 
has completed 676 rotations with a mean period of gh. 55m. 
39°0s., which is almost identical with the periods found during 
the two previous oppositions—viz. gh. 55m. 39'Is. But I am 
hoping to obtain another observation of the spot before the 
planet leaves us for the season. W. F. DENNING 
Bristol, June 28 
Occurrence of ‘‘ Torpedo Marmorata”’ off the Coast of 
Cornwall 
AmoncG the fishes included in the British fauna, but whose 
title to this designation has been considered but doubtfully 
proved, is the Zorfedo marmorata, or a form having the 
spiracles fringed at their edges. It is true that Pennant figures 
this species, but he omits to mention whether his example was 
from the British seas or brought from the French coast by 
Walsh ; and subsequent authors on ichthyology are not suffi- 
ciently precise in their descriptions to enable one to judge of 
which form they are adverting to. All the specimens which I 
have seen in the various British museums have been of the 
cramp fish, with smooth-edged spiracles, 7. modiliana. On 
June 26 an example of 7: marmorata was trawled in Mevagissey 
Bay, and obtained by Mr. Matthias Dunn, who most kindly 
sent it at once to me, and it arrived at Cheltenham on the even- 
ing of the 27th. It was a female, quite fresh, and weighed 
3 lb. 10 oz. ; its length was 174 inches, and its breadth across 
the disk 12 inches. It contained two ova in an early stage of 
development. FRANcIs DAY 
Cheltenham, June 27 
Composite Portraits 
Ir is always desirable to guard new discoveries and inven- 
tions by explicit investigation of the nature of the facts discovered 
and the mode of action of the invention. 
The system of composite portraits ingeniously invented by 
Mr. Galton rightly attracts much attention, and those who have 
had their interest excited by Mr. Galton’s curious portraits of 
thieves, ruffians, and consumptives, will be interested further by 
the portrait of American scientific men in NaTuRF, vol. xxxil. 
p- 176. 
But in using this system as an instrument of discovery it 
must not be hastily assumed that by its means true averages are 
secured. At least, they cannot be averages in every respect 
Take, for example, the hair. The outer limit is determined by 
the greatest extent to which the hair has spread outwards on 
the plate in a number of sitters sufficient visibly to affect it— 
say three or four. But the inner limit is, in the same way, 
determined by the limit in the three or four in whom it stretched 
farthest in. Thus the result must be to give far more than the 
average amount of hair when the portrait is compounded from a 
great number of sitters. 
As regards the nose, the eyes being the fixed starting-points, 
the root of the nose will be nearly a fixed point in the photo- 
graph ; but the tip is limited by shading, and three or four short 
noses will be sufficient to determine where the tip is to be. 
Again, the eyes being fixed points marked on the ground 
glass of the camera, and breadth between the eyes being different 
in different persons, it follows that those who have the eyes near 
together will be photographed on a larger scale than the rest. 
This enlargement will broaden the composite result. But the 
tip of the nose, like the tips of the really long noses, will be lost 
in the dark upper lips of others. 
Proof that [am to an important extent correct in these re- 
marks is to be found in your page of American portraits. They 
present a very remarkable non-American appearance about the 
nostrils, a vertical elongation accounted for by what I have 
pointed out. Also the ears are large and vague, the position of 
the ear relatively to the eye being variable ; and there is a more 
than average breadth of face in three out of the four portraits. 
_Ido not wish to detract from the value of these portraits, 
rightly understood, but assuredly they give prominence to certain 
types of face when these are mixed with others—namely, to 
broad faces with short noses, long lips, large ears, and a super- 
abundance of hair—and it may be useful that attention be 
attracted to this. 
It will be seen that composite portraiture is not suitable for 
anatomical objects whose generic characters are to be recorded 
in explicit statement. But for that and many other purposes, a 
trustworthy though more laborious and less elegant substitute 
may be found by determining the mean positions of a number of 
fixed points in figures accurately obtained. 
JOHN CLELAND 
Ocular Images and After-Images 
Mr. NEWALL’s experiment with the glowing match I have 
been in the habit of performing with my cigar or cigarette, and 
I have become familiar with the lurid ghost he describes, but 
the point that first interested me is one not mentioned in his 
letter, and has reference to the primary serpentine image. This 
I find to consist of a dark red head and a bright yellowish-red 
body—the light viewed at rest being of a mean tint, as if, owing 
to difference in rate of telegraphy, it underwent a process of 
analysis in its movement over the retina. 
I have paid considerable attention to the dying phases of 
powerful retinal impressions, such as result from too bold a gaze 
at the sun or his vicar, the paraffin lamp, and am convinced that 
there is more to record than a mere fading away of a patch of 
colour. On careful scrutiny the patch is seen to be bordered 
with a series of coloured bands, which each in turn overspreads 
it; the order of succession being, unlike that of the primary 
image in the above experiment, towards the red. 
I submit this for confirmation, being conscious that the region 
of these observations is so largely dominated by memory and 
imagination as to render it difficult at times to distinguish the 
psychical from the physiological. W. M. Laurin 
June 25 
A Query as to Swallows 
DuRING a recent stay in Suffolk I found a belief prevalent 
there that swallows lay in necessary stores for their autumn 
migration by packing small flies under the feathers beneath the 
wings. My informant told me that he had shot a swallow once 
in order to ascertain whether this was actually the case; and 
that he had, as he expected, found many small flies beneath the 
down. Knowing how liable swallows are to parasitic invasions, 
IT asked of what kind the flies were, and was told ‘‘ Little gnats, 
and such like.” Is this opinion to be found elsewhere, and is 
there any ground for it ? 
THE COMPOUND LOCOMOTIVE 
“BRS. soon after the compound working of steam in 
marine and stationary engines became an accom- 
plished fact, and the great saving of fuel thereby was 
apparent, the question of applying the compound prin- 
ciple to the locomotive attracted the attention of the loco- 
motive engineers of this and other countries. At first it 
was received with very little favour, which is evident even 
at the present time, there being only two «locomotive 
engineers in this country who are now either trying it 
experimentally or have it permanently in use on the lines 
under their control. This has been mostly caused by the 
idea that the additional gear necessary for the compound 
working with two or more cylinders would render the 
engines more liable to break down. Again it was thought, 
with very good reason, that such engines would have 
great difficulty at starting, for the reason that during the 
first revolution of the driving wheels all the power neces- 
sary to start the engine would have to be generated in 
the high-pressure cylinder. This difficulty was soon sur- 
mounted in engines fitted with only two cylinders working 
compound, by the addition of an arrangement by which 
the engine could be worked as an ordinary locomotive at 
the commencement, and when fairly started the compound 
arrangement could then be applied. 
The usual arrangement adopted in the early trials of 
compound locomotives consisted of two outside cylinders 
of different sizes ; the steam having passed through the 
