54 BULLETIN OF THE BUREAU OF FISHERIES. 
manifested in six of the eight pairs of contrasted figures, the June figures (both for the 
Bay and Sound) being exceptions. 
(4) The average density for Buzzards Bay (1.02314 7%) is lower than that for Vine- 
yard Sound (1.02372) and is particularly low at the head of the Bay. This condition 
is readily understood by reference to the estuaries which discharge into it. 
(5) Certain seasonal differences appear which are, perhaps, of questionable sig- 
nificance. In Vineyard Sound the density figures for the seasons may be arranged in 
the following order: 
MY TUTH Ee ae mci sjoreccs eicls cele crane etoreTetetere Ciao me rassie borate eherrekeretenatsteter stele rarer tscere rare vere nae I. 02339 
Marcha! See Sa hake stata pimard hae toa a te Sotrokatete a loka pminttaerstatatore eralors lets trata the ate I. 02358 
ATR Seeks ehtd Syed IRA SRA Ratt ea ee eee aR oe tO Pal Ste I. 02387 
INOVE mb ees cya 5 ce sisitpesiecs sindeic ferences redthe Saaep dye. etele op aere tolalelal Seep canaden as hens dba aegtaus I. 02403 
For Buzzards Bay the figures can not be given for the entire area, since in March 
only six stations, nearly all of them in the upper half, were visited. Taking the figures 
for these same six stations for the four months we find the following order to obtain: 
I EA ol Be gd Aeros es aller air cree aS Re CaS He ne er RR Rol Cun I. 02266 
AMATI STs eB Atos echt 5 Sutter ts eee mie areas enabled a aAAaN eta (evacra ea erensler inane tareoneeetete I. 02273 
INGVEMIDEL 5) Fs tV5.2 9.5 Ale edd 5 aisle el I ne sea tode! oftte so weve elas) mists einai sete potas I. 02299 
PANTS NS ey asta en ea casey ba co tee ee eB tects ays bt: Sauls alg a siatiodh hate! Aled I. 02327 
The figures for the different seasons were obtained at intervals of about three 
months and by two different observers. Differences due to ‘‘personal equation” 
have thus perhaps played a part in the results. And even if that source of error were 
eliminated, it is quite likely that the figures for the same month in different years would 
not agree at all exactly. In November, 1908, eight of the determinations of the pre- 
ceding November were repeated. The average difference between the earlier and later 
figures was 4 in the fourth decimal place, i. e., a quantity in excess of some of the sea- 
sonal differences appearing in the foregoing tables. 
In order to compare the results of hydrometer readings with those obtained by titra- 
tion for chlorine, 17 water samples were subjected to both tests.2 The chlorine deter- 
mination in each case was compared with the value, computed from Pettersson’s table, 
for water of the specific gravity recorded. It was found that the actual and the expected 
values differed on the average by 1.5 per cent. On the assumption that the figures for 
the titrations were absolutely correct, which is scarcely allowable, this discrepancy 
implies an average error in the salinometer readings amounting to a little over 3 in 
the fourth decimal place. We have thus, in any case, some measure of the accuracy 
of the specific gravity determinations here recorded. As already stated, the fourth 
figure is not entirely trustworthy. It must be remembered, however, that local dif- 
ferences have been pointed out within our region equal to about ten times the amount 
of this average error. 
Seven water samples obtained by us in August, 1909, at points within Nantucket 
Sound and beyond its eastern end, yielded specific gravities varying only from 1.0237 
to 1.0239. These figures are close to, but slightly lower than, those found in Vineyard 
Sound during the same month two years previously. 
a This figure is somewhat too low, since only the upper half of the Bay was represented in the March series. Here, as 
stated, the density is particularly low. 
b These titrations were for the most part made by Dr. W. M. Clark, them a scientific assistant at the Woods Hole 
laboratory. 
