Make boxes contect clearer to interpret

I want to see check the linear relatioship between all the pairs of variables in a dataset. Because i have 39 variables the scatterplot is not very helpful, so i decided to select a random sample of (20 variable) to check it but still chart is too big to interpret. Im using the following code

require("pairsD3")
sample_data <- data[ ,sample(ncol(data), 20)]

pairs(sample_data, pch=19)

and take the following result enter image description here

Is there any way to make the bullets small so i can see if linearity exists or another way to check linearity? Thank you in advance!