unable to force the vector format

Dear all,

I am so ashamed to pollute the list with a trivial question, but it is
a long time I have not used R, and I need a result in the next one or
two hour...

I have a table which I have loaded with read.table, and I want to make
the mean of its columns.

slides <- read.table("slides.txt")
slides [1:5,]

            V1    V2     V3     V4     V5     V6     V7     V8
1 PLB00090AA02 0.147  0.018  0.046  0.064 -0.018 -0.008 -0.063
2 PLB00090BC08 0.171  0.011 -0.001  0.009  0.052  0.032 -0.065
3 PLB00090CG02 0.029 -0.014 -0.042  0.006  0.024 -0.009 -0.043
4 PLB00091AA08 0.033  0.050 -0.022 -0.002  0.038  0.015 -0.037
5 PLB00091BE02 0.183  0.039  0.052 -0.014 -0.034 -0.037  0.037

but I can not get the mean :

mean(slides [1,2:8])

    V2     V3     V4     V5     V6     V7     V8 
 0.147  0.018  0.046  0.064 -0.018 -0.008 -0.063 

obviously, I fail to tell R that I am using a vector.

y<- c(1,2,3,4)
mean(y)

[1] 2.5

but as.vector does not solve my problem

lapply(as.vector(slides[1,2:8]),sum)

$V2
[1] 0.147

$V3
[1] 0.018

$V4
[1] 0.046

$V5
[1] 0.064

$V6
[1] -0.018

$V7
[1] -0.008

$V8
[1] -0.063

In the end, I would like to use lapply to fill a new column in the
table with the means. (and then extract the closest ones to zero...)

Once again, sorry for this mail, whose answer is probably trivial, but
it would be an enormous help if somebody could sent it to me!

-- 
Charles