What does “sheafs” mean in “The rays cut straight sheafs”?

Solution 1:

It appears to be a distinctly technical meaning to sheaf. OED has

6.
a. Physics and Math. A bundle of rays, lines, etc. all passing through a given point.

1863 J. Tyndall Heat ix. §359. 302 A sheaf of calorific rays.
1885 C. Leudesdorf tr. L. Cremona Elem. Projective Geom. 22 A sheaf (sheaf of planes, sheaf of lines) is a figure made up of planes or straight lines, all of which pass through a given point (the centre of the sheaf).
1890 T. H. Eagles Descriptive Geom. 303 Sheafs of rays which in the case of a source of light..form a cone of which that source is the vortex.

Here's such an image. This is rays of sunlight through smoke, but I couldn't find a better representation of the dictionary definition.

Sunlight in Woodland by Keggy

Solution 2:

Noun, not verb

Sheafs is here a plural noun, not a singular verb. There does exist a verb sheaf meaning to bind up into a sheaf or sheaves, but that is not what this instance of the word is.

And you’re right that sheaf has as its oldest sense a bundle of things, usually grains. It appears metaphorically in the familiar Gospel tune “Bringing In the Sheaves”.

What we have here in your quotation is another extended meaning. The OED gives these pertinent senses:

1e. A cluster of jets of fire or water darting up together. (Cf. F. gerbe.)

• 1811 Pinkerton Petral. II. 535 — A thousand sheaves of fire blew up into the air, where, breaking and dispersing, they fell like a shower of stars.
• 1857 Dufferin Lett. High Lat. 125 — A shining liquid column, or rather a sheaf of columns wreathed in robes of vapour, sprung into the air.

But even more likely is this one:

6a. Physics and Math. A bundle of rays, lines, etc. all passing through a given point.

• 1863 Tyndall Heat ix. §359. 302 — A sheaf of calorific rays.
• 1885 Leudesdorf Cremona’s Proj. Geom. 22 — A sheaf (sheaf of planes, sheaf of lines) is a figure made up of planes or straight lines, all of which pass through a given point (the centre of the sheaf).
• 1890 Eagles Descript. Geom. 303 — Sheafs of rays which in the case of a source of light..form a cone of which that source is the vortex.

Sheafs or Sheaves?

As for the variant inflections, sheafs and sheaves alternate. Both are current; I don’t know their relative popularity.

The sheaves form dates from the 16^th century, and sheafs from the 17^th.

In the north of Britain (northern England and Scotland) during the 19^th century and perhaps later could be found dialectal plurals like shoves and shoofs.