cracks on both side of the bay window
If this is an actual bay window in a flat wall, then it's due to a very poor decision to put a bay window in brick or stone, the window is causing too much stress. Brick or stone is great at handling vertical loads, but quite poor at handling lateral loads. A flat window &amp; some brick or stone re-laying &amp; re-pointing will be the only remedy to this type of problem.

Now, if this is actually a whole bay wall that the window simply sits in. Then, that's alarming. Any separation of the bay wall from the building means it's very bad &amp; needs much more than crack patching. You have a rotting foundation under that bay wall from almost a century of trapped moisture weakening the mortar &amp; brick or stone. Unless, it can be determined that the house is collapsing backwards (i.e. multiple wall cracks inside &amp; out), the problem is usually the bay wall tipping out &amp; away from the bottom. The cracks should be wider at the top than at the bottom.

To remedy the bay wall scenario involves installing very beefy temporary supports, jacking the entire bay wall back into place &amp; then re-building the bay wall's foundation. Only after all of that &amp; 30-days mortar curing &amp; effort evaluation do you then re-install &amp; re-point the formerly detached bricks or stones.